ft 


This  book  is  DUE  on  the  last  date  stamped  below. 


1922 


JUL  2  51522 

3       192*' 

MAR  2      195S 
fits  & 


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EASY    EXPERIMENTS 


PHYSICAL    SCIENCE, 


ORAL  INSTRUCTION  IN   COMMON   SCHOOLS, 


LE  ROY   C.    COOLEY,  PH.  !>., 


PROFESSOR   OF   NATURAL    SCIENCE   IN   VASSAR   COLLEGX. 


NEW  YORK   :•  CINCINNATI  •:•  CHICAGO 
AMEKICAN    BOOK     COMPANY 


Entered  according  to  Act  of  Congress,  in  the  year  1871, 

BY  Li.  rCOT   C.  COOLEY. 
In  the  Office  of  the  Librarian  of  Congress  at  Washington. 


C77 


PEEFAGE. 


IT  is  coming  to  be  very  generally  believed  by  educators 
that  one  of  the  most  important  aims  of  primary  instruc- 
tion should  be  to  discipline  the  child  to  habits  of  quick 
and  accurate  observation,  and  to  the  power  of  making  sim- 
ple but  correct  inferences  from  the  facts  which  his  senses 
reveal.  Surely  this  result  can  be  reached  more  easily  by 
means  of  those  facts  which  nature  communicates  through 
the  senses  than  by  subjects  which  have  no  natural  depend- 
ence upon  material  forms ;  and  hence  the  superior  adap- 
tation of  the  simple  facts  of  physical  science  to  the  want? 
of  common-school  instruction. 

But  the  only  way  to  strengthen  mind  is  to  make  it 
work.  If  the  senses  are  to  be  developed  and  disciplined, 
the  child  must  be  allowed,  and,  if  need  be,  compelled,  to 
use  his  senses  for  himself.  The  teacher  is  to  guide  him, 
but  not  to  carry  him.  His  mind  is  to  be  directed  toward 
material  things,  and  taught  to  see  their  forms  and  charac- 
ters as  they  themselves  present  them.  The  instructor  is 
to  be  his  guide,  but  Nature  is  herself  to  be  his  teacher. 
The  intelligent  teachers  of  common-schools  are  eagerly 
asking  how  can  this  theory  be  wrought  into  practice. 
Lack  of  time  and  lack  of  material  seem  to  almost  forbid 


iv  PREFACE. 

the  attempt :  lack  of  time,  because  custom  and  public 
opinion  demand  so  much  knowledge  of  books  in  all  the 
branches  which  overcrowd  the  primary  course ;  and  lack 
of  material,  because  apparatus  other  than  a  blackboard 
and  a  few  maps  is,  in  most  common -schools,  a  thing  un- 
heard of.  It  is  pleasant  to  anticipate  a  time  when  the 
higher  and  theoretical  parts  of  arithmetic  and  grammar 
shall  be  reserved  for  the  high-school  course  of  study,  and 
their  places  in  the  common-school  left  to  the  more  appro- 
priate study  of  nature.  It  is  pleasant  to  anticipate  the  time 
when  every  common-school  shall  be  provided  with  an  ap- 
propriate set  of  apparatus,  through  which  Nature  may  teach 
her  simple  truths  to  children  in  her  own  playful  and  child- 
like manner.  The  time  is  doubtless  coming  when  both 
these  anticipations  will  be  realized,  and  all  the  quicker 
will  it  come  if  teachers  will  only  leyin  the  work  by  using 
the  very  little  time  and  means  already  at  their  disposal. 
Some  have  already  begun  :  they  find  it  possible  to  secure 
time  for  a  short  exercise  each  day,  or  at  least  two  or  three 
times  a-week,  in  which  they  perform  simple  experiments 
with  such  objects  and  utensils  as  they  find  at  hand,  much 
to  the  delight  and  profit  of  their  schools.  Letters  from 
several  of  these  announce  their  surprise  at  the  interest 
thus  aroused,  not  only  among  pupils,  but  among  parents 
also.  "Whole  neighborhoods  are  in  some  instances  awak- 
ened, and  it  will  not  be  difficult  in  such  cases  to  obtain 
money  for  the  purchase  of  better  means  of  illustration  ! 
Now  this  little  book  is  offered  as  an  aid  to  the  teachers 


PREFACE.  v 

who  are,  or  who  desire  to  be,  engaged  in  this  work.  It 
is  made  up  of  experiments  of  the  simplest  kind,  which, 
with  few  exceptions,  can  be  performed  with  such  appa- 
ratus as  can  be  collected  anywhere  almost  without  expense. 
These  experiments  are  arranged  in  groups,  each  group 
teaching  some  elementary  tact  or  principle  of  science. 
They  are  selected  from  among  those  which  the  writer  has 
long  been  using  in  the  earliest  stages  of  his  instructions 
to  his  classes,  and  which  are  now  being  reproduced  by 
young  teachers  who  have  gone  out  into  the  public-schools 
of  the  State,  and  from  whom  reports  of  abundant  success 
are  received.  There  is,  therefore,  good  reason  to  believe 
that  they  are  practical  and  instructive. 

But  there  is  another  purpose  which  this  little  book  is 
designed  to  serve.  The  best  teachers  of  natural  science 
are  unanimously  of  the  opinion  that  the  very  best  results 
can  be  secured  only  by  allowing  the  student  to  make 
experiments  for  himself.  In  the  study  of  science  in  high- 
schools  and  academies,  good  text-books  are  very  desirable ; 
a  full  course  of  illustrative  experiments  by  the  teacher  is 
indispensable;  but  if,  added  to  these,  there  can  be  a  course 
of  simple  experiments  by  the  pupils  themselves,  the  value 
of  both  will  be  enhanced. 

Now  the  experiments  described  in  the  following  pages 
are  such  as  intelligent  boys  and  girls  can  make  with  little 
or  no  assistance.  All  that  the  teacher  need  to  give  them 
is  encouragement,  and  it  is  believed  that  he  would  find 


V\  PREFACE. 

his  own  work  more  productive  if,  in  addition  to  the  text- 
book and  his  lectures,  this  course  of  simple  experiments 
could  be  put  into  the  hands  of  every  pupil  in  his  class. 
Students  can  not  too  early  begin  to  acquire  the  habit  and 
the  power  of  verifying  the  statements  in  the  science  which 
they  study.  This  they  can  do  in  an  elementary  course  of 
study  by  experiments  of  the  simplest  character  made  with 
apparatus  the  most  inexpensive. 


APPARATUS. 


THE  following  list  comprises  the  most  important  pieces 
of  apparatus  needed  for  the  performance  of  the  experi- 
ments described  in  this  book.  The  articles  named  in  the 
second  column  may  be  obtained  very  cheaply  of  apparatus 
dealers :  those  in  the  first  can  be  found  at  home  in  any 
district,  A  great  many  other  things  will  be  used,  but 
they  are  too  common  to  need  even  to  be  named  here. 

Fruit-cans.  Glass  tubing— £  Ib.  ass'd  sizes. 

Ale-glasses.  Rubber  tubing — 2  ft. 

Bottles.  Alcohol  lamp. 

Corks.  Flask— glass,  1  pt. 

Plates.  Test  tubes— J  doz.  6  inch. 

File.  Convex  lens. 

Funnel.  Violin  string. 

Tuning-fork.  Glass  tube — for  fractional  elec. 

Shot.  Sealing-wax. 

Besides  this  apparatus  some  chemicals  are  ^scessary. 
All  these,  except  some  which  are  too  common  to  need 
mentioning,  are  comprised  in  the  following  list.  They 
may  also  be  obtained  of  the  apparatus  dealers  at  very 
trifling  expense. 

Alcohol.  Sulphuric  acid. 

Cochineal.  Hydrochloric  acid. 

Litmus.  Nitric  acid. 

Sulphur.  Ammonia. 

Copper  clippings. 


EAST    EXPERIMENTS 


NATURAL    PHILOSOPHY. 


"Always  bear  in  mind  that  the  simplest  experiments,  or  those  most 
easily  imitated  by  the  pupils,  are  the  best." — Nature. 


INTRODUCTION". 


Divisibility.  Ex.  I.— Take  a  glass  jar,  holding  half  a 
gallon, — a  fruit-can  answers  the  purpose  well, — and  till  it 
with  water.  Next  take  a  little  powdered  cochineal,  as 
much  as  will  lie  upon  the  end  of  a  penknife-blade,  which 
will  not  be  more  than  half  a  grain  by  weight,  and  dissolve 
it  in  a  thimbleful  of  water.  Finally  pour  the  cochineal 
into  the  clear  water  in  the  jar.  Notice  the  cloud-like 
masses  of  colored  water  slowly  making  their  way  down- 
ward. After  a  little  time  stir  the  water  briskly,  and  then 
see  that  every  part  of  it  is  distinctly  colored. 

Now  it  is  said  that  there  are  as  many  as  30,000  drops 
of  water  in  a  half-gallon,  and  that  it  must  take  as  many 
as  100  little  particles  of  the  cochineal  to  color  a  single 
drop  distinctly. 

In  this  experiment,  then,  a  single  half-grain  weight  of 
cochineal  has  been  divided  into  not  less  than  3,000,000 
pieces. 

J5».  £•— Place  a  goblet  on  the  table  and  fill  it  about 
one  half  full  of  water.  Take  a  piece  of  loaf-sugar  as  large 
as  a  walnut,  and  by  blows  break  it  into  small  pieces. 
Put  these  pieces  into  the  water  and  stir  them  about  vig- 
orously. After  a  little  time  notice  that  the  sugar  has 
entirely  disappeared. 

In  this  case  the  body  has  been  divided  into  pieces  so 
small  that,  being  colorless,  they  can  not  be  seen  at  all. 


12  INTRODUCTION. 

Ex.  3.— Take  a  small  piece  of  marble,  and  by  pounding 
it  reduce  it  to  the  finest  powder:  the  separate  grains  are 
almost  invisible,  and  yet  each  one  of  them  is  a  piece  of 
the  original  block. 

We  learn  from  these  experiments  that  some  bodies  can 
be  separated  into  many  parts.  And  when  we  think  of 
others  which  we  have  not  just  now  tried,  we  remember 
that  they  too  can  be  broken  or  cut  into  pieces.  Now  this 
quality  of  matter,  by  virtue  of  which  bodies  may  he  sepa- 
rated into  pieces,  is  called  divisibility. 

REMARKS. — Teachers  will  notice  that  the  descriptions 
of  the  foregoing  experiments  are  minute  and  clear  enough 
to  forbid  any  failure  in  the  performance  of  them.  But 
these  descriptions  only  show  the  work  which  teachers 
must  do ;  they  do  not  give  the  language  which  they  must 
use.  While  making  an  experiment  the  teacher  ought,  by 
skillful  questions  and  appropriate  remarks,  to  keep  the 
attention  of  the  children  upon  it,  so  that  every  part  of  the 
apparatus  shall  be  observed  and  every  action  definitely 
seen.  Above  all  things  ought  care  to  be  taken  that  the 
final  inference  is  seen  to  be  the  natural  consequence  of  the 
facts  observed  in  the  experiments.  The  tendency  will 
doubtless  be  for  the  teacher  to  do  all  the  talking,  while 
the  pupils  rest  contented  with  simply  repeating  what  they 
hear.  This  should  be  avoided. 

The  pupils  should  themselves  be  made  to  describe  the 
apparatus  while  they  look  at  it  •  to  announce  the  results 
as  they  occur  ;  and  to  interpret  them  as  fully  as  possible 
and  with  as  little  assistance  as  may  l>e  practicable. 

No  two  intelligent  teachers  will  ever  work  by  exactly 
the  same  method,  but  yet  the  principle  just  stated  ought 
to  be  the  foundation  of  every  plan  and  determine  the 


INTRODUCTION.  13 

detail  of  every  attempt  to  teach  science,  in  its  most  ele- 
mentary forffij  for  which  these  experiments  are  designed. 
The  following  conversation  occurred  between  a  teacher 
and  his  class  in  regard  to  the  experiments  just  described. 
It  will  serve  to  illustrate  the  method  of  making  the  pupil 
use  Ms  senses  to  acquire  knowledge. 

TEACHEE. — I  have  here  three  substances  about  which 
we  want  to  learn  something  to-day.  One  of  them — this 
which  you  see  (holding  it  up  in  view  of  the  class) — is 
cochineal;  another  (showing  it)  is  a  lump  of  loaf-sugar; 
and  the  third  (showing  it  also)  is  a  piece  of  marble.  I 
want  to  show  you  some  things  that  can  be  done  with 
these,  and  I  would  like  to  have  you  to  tell  me  exactly 
what  you  see  and  learn. 

1st  Experiment.— Now  notice  (teacher  takes  a  half- 
gallon  jar  and  fills  it  with  water) :  what  have  we  here  ? 

PUPILS.-  -A  jar  of  water. 

TEACHER. — I  must  tell  you  now  that  the  jar  holds  one 
half  a  gallon ;  and  now  think  a  moment,  whether  you 
have  not  often  seen  water  that  looked  very  unlike  this. 
Tell  me,  then,  what  you  see  before  you. 

A  FEW  PUPILS. — A  half-gallon  of  clear  water  in  a  jar. 

TEACHER. — Yes;  you  all  can  see  that  the  water  is  not 
muddy  nor  colored  ;  it  is  clear,  and  you  know  I  told  you 
that  the  jar  holds  half  a  gallon. 

Now  here  (dipping  up  a  little  cochineal  upon  his  knife- 
blade)  is  the  cochineal.  It  was  not  always  as  you  see  it 
now.  It  was  found  in  the  shape  of  little  balls  about  as 
large  as  large  shot,  each  covered  with  a  grayish  coating  ; 
but  now  what  do  you  say  of  it? 

PUPILS. — A  reddish  powder. 

TEACHER. — The  little  balls  have  been  broken  into  pieces 


H  INTRODUCTION. 

— indeed,  crushed  into  this  line  powder.  But  see  what  I 
will  do  with  it.  Just  the  little  on  my  knife — there  is  not 
more  than  the  weight  of  half  a  grain — remember  this, 
I  will  nse  in  this  way  (putting  a  little  water  into  a 
goblet  and  the  powder  into  it,  and  thoroughly  stirring 
them  together).  Now,  John,  come  and  look  at  this,  and 
tell  your  mates  whether  yon  can  see  the  powder 

JOHN. — There  is  a  little  at  the  bottom. 

TKACHER. — Just  a  little  ;  but  where  is  all  the  rest  ? 

JOHN. — It  looks  like  red  water. 

TEACHER. — Yes;  you  do  not  see  the  powder  in  the 
water,  but  the  water  looks  red  because  the  little  particles 
of  powder  are  broken  up  into  such  very  little  pieces  that 
John  could  not  see  them,  and  these  little  pieces  are  scat- 
tered throughout  every  part  of  the  water. 

But  now  look  again  (pouring  the  "red  water"  into  the 
jar) :  who  will  tell  me  what  is  going  on  now  ? 

SEVERAL  PUPILS. — The  cochineal  is  going  to  the  bot- 
tom! 

OTHERS. — It  is  mixing  with  the  water! 

TEACHER. — When  we  have  watched  these  very  pretty 
cloud-like  streams  of  colored  water  long  enough,  I  will 
stir  the  water  thoroughly  in  the  jar  (doing  so  after  a 
pause).  Now  tell  me  if  you  see  any  change  made  in  the 
water. 

PUPILS. — It  is  red  now,  all  through  ! 

TEACHK:?. — But  you  know  there  was  a  whole  half- 
gallon  of  water  and  only  half  a  grain  of  cochineal ! 
Now  let  us  see, — how  many  drops  of  water  do  you  sup- 
pose tli<  re  i  in  the  jar?  Of  course  you  do  not  know, 
and  I  wi  1  bell  you  that  it  is  said  that  there  are  not  less 
than  30,0  '  >.  It  is  thought,  too,  that  it  would  need  as 
many,  at  least,  as  100  little  pieces  of  cochineal  to  color  a 


INTRODUCTION.  15 

single  drop,  perfectly  in  every  part  of  it.  And  yet  the 
half-grain  has  colored  the  half-gallon  ! 

Now  who  will  answer  quickly, — If  it  take  100  pieces 
of  cochineal  to  color  one  drop  of  water,  how  many  pieces 
will  it  take  to  color  30,000  drops  ? 

PUPILS. — One  hundred  times  30,000  are — (after  hesita- 
tion a  few  answer  correctly)  3,000,000. 

TEACHER. — That  is  right.  Now  look  again  at  this 
water:  it  is  crimson-colored, — every  drop  of  it.  Into 
how  many  pieces  does  this  experiment  show  the  half- 
grain  of  cochineal  to  be  divided? 

MANY  PUPILS.— Into  3,000,000  pieces ! 

TEACHER. — Surely  it  was  a  very  little  thing  to  be  broken 
up  into  such  a  multitude  of  pieces  !  But  now  for  the 

2d  Experiment. — Let  us  use  this  little  lump  of  sugar. 
What  have  we  here  ?  (Placing  a  goblet  on  the  table  and 
half  filling  it  with  water). 

PUPILS. — A  goblet  of  water. 

TEACHER. — Now  watch  the  sugar  (dropping  it  into  the 
water  and  stirring  it  about  a  little  time).  Well,  what  has 
happened  ? 

PUPILS. — It  has  fallen  to  pieces. 

TEACHER. — I  will  continue  stirring  these  pieces  about  in 
the  water  (doing  so  until  the  sugar  is  dissolved) ;  and  now 
can  you  see  them  ?  Come  and  look.  (To  those  who  came) 
Well,  where  is  the  sugar  ? 

PUPILS. — It  is  in  the  water. 

TEACHER. — But  can  you  see  it? 

PUPILS. — No. 

TEACHER. — How  then  do  you  know  that  it  is  in  the 
water  ? 

PUPILS. — We  saw  you  put  it  in  there. 

TEACHER.— Yery  good:  you  saw  it  put  there,  and  it  has 


16  INTRODUCTION. 

not  been  taken  out  again.  But  you  did  see  it  in  the  water 
at  first :  why  can  you  not  see  it  now  ? 

PUPILS. — Because  it  is  broken  up  and  all  scattered 
through  the  water. 

TEACHER. — That  is  it  exactly  !  And  now  you  can  tell 
me  what  this  experiment  shows  us  about  sugar,  can  you 
not? 

PUPILS. — That  sugar  can  be  broken  up  into  very  little 
pieces. 

TEACHER. — Yes;  or  you  might  say, — it  shows  us  that 
sugar  can  be  divided  into  pieces  which  are  so  small  that 
they  can  not  be  seen. 

Now  let  us  see  about  the  marble. 

3d  Experiment.— George,  now  I  place  the  marble  upon 
this  brick  which  I  have  brought  here  on  purpose;  won't 
you  come  and  strike  it  with  this  hammer  ?  (He  does  so.) 
There,  what  have  you  done  to  the  marble  ? 

GEORGE. — I  have  broken  it. 

TEACHER. — Now  take  one  of  the  pieces  and  strike  it. 
(He  does  so.)  There,  what  have  you  done  to  the  piece  ? 

GEORGE. — Crumbled  it  all  to  powder. 

TEACHER. — But  not  to  very  fine  powder ;  but  now  sup- 
pose you  strike  these  little  pieces,  will  they  be  broken 
again"?  Try  it,  George.  (He  does  so.)  Well  ? 

GEORGE. — The  powder  is  fine  now. 

TEACHKR. — Then  you  must  have  broken  the  little  pieces 
up  into  still  smaller  ones.  We  can  hardly  see  them  sepa- 
rately. And  now,  scholars,  tell  me  what  all  this  shows 
about  marble. 

PUPILS. — That  marble  may  be  divided  into  little  pieces. 

TEACHKR. — Very  good.  "We  have  now  tried  three 
things, — cochineal,  sugar,  and  marble.  We  have  found 
that  each  may  be  divided  into  very  little  parts.  They 


INTRODUCTION.  17 

are  alike  in  this  respect,  even  though  so  very  different  in 
most  others.  This  quality  of  these  bodies,  which  allows 
thetn  to  be  broken  or  separated  into  parts,  is  called 
divisibility.  Can  you  think  of  other  substances  which 
can  be  divided  ?  (Several  things  are  quickly  mentioned.) 
All  these  things  have  the  same  quality  as  you  have  seen 
the  cochineal,  the  sugar,  and  the  marble,  to  possess.  What 
is  that  quality  called  ? 

PUPILS.  — Di  visi  bi  lity. 

TKAOHKB. — What,  then,  does  this  word, — divisibility, — 
mean  ?  I  will  write  its  meaning  on  the  blackboard  for 
you. 

"  Divisibility  is  that  quality  of  bodies  which  allows 
them  to  be  cut  or  broken  into  parts." 

Perhaps  no  other  teacher  would  do  just  exactly  as  this 
one  did,  in  conducting  this  exercise,  but  in  some  respects 
his  example  is  worthy  of  careful  imitation. 

1st.  He  evidently  had  a  definite  plan  marked  out 
beforehand.  No  teacher  should  attempt  a  single  experi- 
ment until  he  has  tried  it,  studied  it,  and  formed  his  plan 
for  using  it. 

2d.  His  object  seemed  to  be  to  make  the  pupils  see 
clearly  what  occurred,  and  to  infer  correctly  from  what 
they  saw.  Let  every  teacher  lay  every  plan  and  work  out 
every  detail  with  direct  reference  to  these  two  results. 

3d.  Hence  he  called  upon  his  pupils  to  tell  him  what 
things  were  being  used  and  what  effects  produced,  instead 
of  describing  them  hiv)9rlf.  So  should  every  teacher  do, 
telling  the  pupils  only  those  things  which  the  apparatus 
does  not  clearly  show. 

It  will  be  found  to  be  an  excellent  plan,  especially  after 


18  INTRODUCTION. 

pupils  have  had  some  experience  in  these  exercises,  to 
first,  put  before  them  all  the  apparatus  for  an  experiment 
ready  for  use  and  ask  some  one  pupil  to  describe  it  fully, 
then  to  make  the  experiment  deliberately  and  silently, 
afterward  calling  upon  a  second  pupil  to  tell  you  what 
you  did,  and  upon  a  third  to  tell  you  what  changes  or 
effects  he  saw  produced,  and  upon  a  fourth  to  tell  you 
what  he  thinks  the  experiment  teaches.  Eepeat  the  ex- 
periment, if  need  be,  to  bring  out  any  essential  point 
which  the  pupils  did  not  at  first  discover. 

It  will  also  be  well  to  encourage  the  pupils  to  make  ex- 
periments for  themselves.  Call  upon  individuals  to  help 
you  at  times.  Especially  if,  during  an  exercise,  one  is  seen 
to  be  inattentive,  nothing  can  be  better  than  to  ask  him 
to  help  you  in  the  experiment  being  made.  Let  him  do 
some  part  of  it  which  you  know  he  can  do  well,  and  take 
care  that  he  do  not  fail.  His  success  will  do  more  than 
any  thing  else  can  to  secure  his  attention  in  the  future. 

The  following  experiments  furnish  abundant  material 
for  such  exercises  as  have  just  been  indicated.  If  used  at 
all  in  common-schools,  they  can  not  fail  to  awaken  lively 
interest  among  the  scholars,  and  will  always  leave  their 
minds  in  better  condition  to  pursue  their  regular  studies 
to  better  advantage.  If  used  skillfully  by  the  methods 
just  pointed  out,  their  own  educational  value  will  not  be 
surpassed  by  that  of  any  other  branch  of  study. 


THE    PROPERTIES    OF    MATTER. 


Impenetrability.  Experiment  4.— A  glass  jar  may 
be  partly  filled  with  water  (Fig.  1).  Let  a  block  of  wood 
of  convenient  size  and  shape  be  then  pushed 
down  into  the  water.  Notice  that  as  the 
wood  enters,  the  liquid  rises  in  the  jar,  and 
that  it  falls  again  when  the  wood  is  taken 
out.  We  see  that  these  two  bodies,  wood  and 
water,  can  not  be  put  into  the  same  place  at 
the  same  time. 

Ex.  5. — Let  an  inverted  goblet  be  held 
^  1-  with  its  mouth  on  the  surface  of  the  water 
in  the  jar.  Notice  that  the  goblet  is  full  of  air.  Next, 
push  the  goblet  down  into  the  water.  Notice  that  the 
goblet  is  still  full  of  air,  the  water  not  rising  into 
it.  We  see,  here,  that  water  and  air  can  not  be 
put  into  the  same  place  at  the  same  time. 

Ex.  6.— Hold  the  inverted  goblet  in  the  water 
as  before,  its  mouth  being  an  inch  or  more  under 
the  surface.      Having   a   large    cork,  fixed    upon 
the  end  of  a  bent  wire  (Fig.  2)  for  a  handle,  push  U 
it  down  under  the  edge  of  the  goblet   and  then 
up  into  the  air  within.     Notice  that  as  the  cork    Fig'2' 
goes   up  into   the   air  some  air  bubbles  escape  through 
the  water.     We  see  that  air  and  cork  can  not  be  put  into 
the  same  place  ;it  the  same  time. 


20  PHYSICAL   SCIENCE. 

What  is  seen  in  these  experiments  is  true  of  all  bodies ; 
no  two  can  be  put  into  the  same  place  at  the  same  time. 
This  property  of  matter,  by  which  no  two  bodies  can 
occupy  the  same  space  at  once,  is  called  impenetrability. 

Indestructibility.  Ex.  7. — into  a  small  tin  cup  put 
a  little  line  sugar  and  carefully  weigh  them.  (See  Ex.  32, 
Fig.  7.)  Add  water  enough,  afterward,  to  dissolve  the 
sugar.  Notice  that  the  sugar  has  all  disappeared.  Next 
place  the  cup  over  a  stove  or  a  lamp-flame,  and  continue 
the  heat  until  the  water  is  driven  away  and  the  cup  and 
its  contents  are  thoroughly  dry,  taking  care  that  nothing 
is  lost  by  boiling  or  flying  over.  Notice  that  the  sugar  is 
to  be  seen  in  the  cup  again.  Finally  weigh  the  cup  and 
its  sugar ;  the  weight  should  be  the  same  as  before  the 
sugar  was  dissolved.  We  see  that  sugar  may  disappear 
without  being  destroyed. 

Whenever  any  substance  disappears  from  any  cause,  its 
form  is  changed,  but  the  substance  is  never  destroyed. 
This  property  of  matter,  by  virtue  of  which  it  can  not  be 
destroyed,  is  called  indestructibility. 

Elasticity.  Ex.  8. — Take  a  piece  of  steel  wire  and 
hold  one  end  firmly  in  one  hand.  With  the  other  hand 
take  hold  of  the  other  end  and  pull  it  over  to  one  side. 
Notice  that  the  wire  yields  to  the  force  of  the  hand. 
Next,  let  go  the  end  which  has  been  pulled  away,  and 
notice  that  it  springs  back  to  its  former  place.  We  see 
that  this  wire  will  yield  to  a  force  and  spring  back  again 
when  the  force  is  taken  away. 

Ex.  9. —  Having  a  glass  ball — an  "agate"  used  by 
boys  in  playing  "marbles" — drop  it  upon  a  stone  or  other 
hard  surface.  Notice  that  it  bounds  upward  to  consider- 


PROPERTIES   OF   MATTER.  21 

able  height.  Now  the  ball  bounds  because  it  is,  for  the 
moment,  flattened  a  little  just  where  it  strikes  the  stone, 
but  at  the  next  instant  it  springs  back  to  its  former  shape, 
and  this  springing  back  throws  the  ball  upward.  This 
being  so,  we  see  that  even  glass  will  yield  to  a  force  and 
afterward  spring  back. 

This  property  of  bodies,  shown  by  the  wire  and  the 
glass,  by  which  they  spring  back  to  their  former  position 
or  shape  after  having  yielded  to  some  force,  is-  called 
elasticity \  All  bodies  are  more  or  less  elastic. 

Ductility.  Ex,  10. — Hold  the  middle  of  a  small  glass 
tube  in  the  flame  of  an  alcohol  lamp  until  about  an  inch 
of  its  length  is  made  red-hot.  It  will  be  necessary  to  roll 
the  tube  over  in  the  flame  constantly  to  heat  it  on  all  sides 
alike.  When  heated  to  redness,  take  it  from  the  flame, 
and  at  the  same  time  pull  with  both  hands  lengthwise  of 
the  tube.  Notice  that  the  glass  is  drawn  out  into  a  long 
and  thread-like  wire. 

Many  substances,  like  glass,  may  be  drawn  out  into 
wire.  Metallic  wires  are  very  common.  The  property 
of  matter  by  which  a  body  can  be  drawn  into  wire  is 
called  ductility. 

Ex.  11. — Taking  hold  of  the  ends  of  the  glass  still 
attached  to  the  wire,  use  them  as  handles,  and  on  moving 
them  about,  notice  how  flexible  line  threads  of  glass  are. 

Ex.  12. — Break  one  handle  off,  leaving  the  fine  wire 
still  attached  to  the  other.  Put  the  fine  end  down  deep 
into  a  vessel  of  water  and  the  other  end  in  the  mouth. 
Blow  strongly,  and  notice  the  bubbles  of  air  coming  in  a 
steady  stream  up  through  the  water,  showing  that  the  fine 
thread  is  still  a  glass  tube.  It  can  not  be  drawn  so  fine  as 
not  to  be  a  tube. 


22  PHYSICAL  SCIENCE. 

Combustibility.  Ex.  13. — Take  as  much  potassic 
chlorate  as  may  lie  upon  a  penny  and  mix  it  with  an 
equal  quantity  of  sugar.  Put  this  mixture  upon  a  piece 
of  card-board  resting  on  the  top  of  a  goblet.  Add  next 
two  or  three  drops  of  strong  sulphuric  acid,  and  quickly 
take  the  hand  away  from  over  the  mixture.  Notice 
that  a  violent  and  surprising  combustion  immediately 
follows. 

Wood,  coal,  oil,  and  many  other  bodies  burn  freely. 
This  property  of  matter,  by  which  it  is  able  to  burn,  is 
called  combustibility. 

Explosibility.  Ex.  14. — Let  as  much  potassic  chlo- 
rate as  may  lie  on  the  point  of  a  penknife-blade  be  put 
into  a  mortar  with  the  same  quantity  of  sulphur.  Larger 
quantities  can  not  be  safely  handled.  Next  rub  the  mix- 
ture with  the  pestle.  Notice  a  sharp  report  or  perhaps 
several  reports  in  succession  if  the  rubbing  be  continued. 

Gunpowder  will  explode  when  touched  with  a  burning 
match,  and  some  other  substances  have  the  same  property. 
This  property  of  substances,  by  which  they  may  be  made 
to  explode,  is  called  cxploaibility. 


ATTRACTION. 


Gravitation.  Ex.  15. — Let  a  ball  be  dropped  from 
the  hand.  Its  falling  toward  the  earth  is  an  example  of 
what  is  seen  perhaps  every  day  of  our  lives.  All  bodies 
fall  toward  the  earth. 

But  not  only  is  this  true ;  the  astronomer  finds  also  that 
all  the  heavenly  bodies  are  pulling  each  other  toward 
themselves.  Indeed,  all  bodies  tend  to  approach  each 
other.  The  attraction  which  pulls  them  toward  each 
other  is  called  gravitation. 

Cohesion.  Ex.  16.— Take  a  half-sheet  of  letter-paper 
and  gum  each  end  to  a  smooth  bar  of  wood  longer  than 
the  width  of  the  paper,  so  that  each  end  will  project  be- 
yond the  edge.  (Fig-  3.)  Let  the  bars 
be  exactly  parallel.  Now  with  the  pro-  I 
jecting  bars  as  handles,  two  persons  j 
may  try  to  pull  the  paper  apart.  An 
astonishing  force  will  be  needed  to  do  it 
when  the  pull  is  steady  and  square. 
Notice  that  the  parts  of  the  paper  are  M 
held  together  very  firmly.  We  see  that  Fi<r  3 

there  is  an  attraction  among  its  parts. 

Ex.  17.— An  apple  being  cut  into  two  halves,  let  their 
fresh  surfaces  be  pressed  together  again,  and  notice  how 
hard  it  is  to  pull  them  apart  again  afterward.  We  see 
that  there  is  attraction  between  them. 


24  PHYSICAL   SCIENCE. 

Ex.  18.— Let  two  ouJlets  be  flattened  and  then  smoothed 
on  one  side  of  each  with  a  knife  until  they  will  fit  each 
other  closely.  Next  press  the  two  freshly-cut  surfaces 
firmly  together,  and  afterward  let  them  be  pulled  apart 
again.  Notice  that  it  needs  considerable  force  to  pull 
them  apart. 

In  all  these  experiments  we  notice  an  attraction  between 
parts  of  one  body  or  of  two  bodies  of  the  same  kind  of 
matter.  Now  the  attraction  which  holds  the  parts  of  a 
body  or  of  different  bodies  of  the  same  kind  together  is 
called  cohesion. 

Adhesion.  Ex.  19.— Having  two  test-tubes,  or  even 
two  small  cups,  put  some  oil  into  one  and  some  mercury 
into  the  other.  Into  the  oil  plunge  a  rod  of  wood  and 
into  the  mercury  another.  Now  taking  the  wood  from 
the  oil,  we  notice  it  covered  with  a  film  of  that  substance. 
Next  take  the  wood  from  the  mercury,  and  notice  not  a 
drop  of  the  liquid  upon  it.  We  learn  that  there  is  an  at- 
traction between  wood  and  oil,  while  none  is  shown  be- 
tween wood  and  mercury. 

Ex.  20. — Have  two  cups  of  water:  into  one  of  them 
plunge  a  rod  of  wood,  into  the  other  a  piece  of  wax,  or 
even  a  candle.  On  taking  them  out,  notice  that  water 
clings  to  the  wood,  and  wets  it,  but  not  to  the  wax  or 
candle.  We  learn  that  there  is  an  attraction  between 
wood  and  water,  but  apparently  none  or  very  little  be- 
tween wax  and  water. 

Ex.  21. — Draw  a  crayon  along  the  surface  of  the  black- 
board, and  notice  its  particles  clinging  thereto. 

We  learn  from  these  experiments  that  there  is,  in  some 
cases,  an  attraction  between  different  kinds  of  matter 
which  holds  their  particles  together.  This  attraction, 


ATTRACTION.  25 

which  holds  particles  of  different  kinds  together,  is  called 
adhesion.     In  some  cases  it  is  called  capillary  force. 

Capillary  Force.  Ex.  22.— Let  some  water  be 
colored  with  ink,  or,  far  better,  with  cochineal.  Take  a 
small  glass  tube — its  diameter  not  more  than  ^  of  an 
inch — and  put  one  end  of  it  into  the  colored  liquid. 
Notice  the  liquid  springing  up  into  the  tube  quickly 
and  remaining  there  much  higher  than  it  is  outside. 

Ex.  23. — Stand  a  piece  of  flat  glass  in  the  water,  and 
notice  the  liquid  rising  a  little  way  up  along  its  sides. 

Now  the  attraction,  shown  in  these  experiments,  by 
which  a  liquid  is  lifted  in  small  tubes  or  along  the  sides 
of  solid  bodies,  is  called  cap IWi ry  force. 

Ex.  24. — Wrap  a  common  bottle  in  a  strip  of  blotting- 
paper  which  is  as  wide  as  the  bottle  is  high,  and  fasten  its 
edges  with  wax.  Next  fill  the  bottle  with  water  made 
black  by  ink.  Finally,  stand  the  bottle,  thus  prepared, 
on  a  common  dinner-plate,  and  pour  water  upon  the  plate 
to  come  in  contact  with  the  lower  edge  of  the  paper  on 
the  bottle.  Notice  that  the  water  will  be  soon  seen  slowly 
rising  up  the  paper,  and  in  a  little  time  it  will  have 
climbed  to  the  top  of  the  bottle. 

Remember,  also,  that  oil  rises  in  a  lamp-wick  in  the 
same  way ;  that  water  will  wet  a  piece  of  cloth  through- 
out in  a  little  time,  if  only  one  corner  touches  the  liquid  ; 
that  ink  spreads  on  blotting-paper,  and  other  similar  and 
familiar  facts.  In  all  these  cases,  as  in  the  experiment, 
capillary  force  is  causing  a  liquid  to  penetrate  porous 
solids. 

Ex.  25. — Having  two  strips  of  glass — three  inches 
long  by  an  inch  in  width  is  a  convenient  size — put  a  nar- 
row piece  of  card-board  between  their  ends,  and  then 


PHYSICAL   SCIENCE. 


cement  them  together  with  a  little  sealing-wax.  The  two 
plates  are  then  parallel  and  very  near  together — separated 
only  by  the  thickness  of  the  card-board.  Take  the  sealed 
end  in  the  hand  and  bring  the  other  end  of  the  plates 
down  into  some  colored  water.  Notice  the  fluid  instantly 
leaping  up  to  some  height,  where  it  remains  between  the 
plates. 

Ex.  26. — Cement  two  other  similar  plates  of  glass  so 
that  they  shall  not  be  parallel — one  edge  of  the  pair 
being  in  contact,  the  other  edges  being  separated  perhaps 
an  eighth  of  an  inch.  Put  the  lower  end  of  this  pair  of 
plates  into  the  colored  water;  it  will  spring  up  quickly 
as  before.  But  notice  that  its  surface  is  in  the  form 
of  a  beautiful  curve  (Fig.  4),  and  farther,  that  the  liquid 
is  lifted  highest  where  the  plates  are  nearest 
together. 

Ex.  27. — Select  two  small  glass  tubes, 
one  of  which  shall  have  a  diameter  twice 
as  great  as  the  other.  Put  one  end  of  each 
into  the  colored  water  and  it  will  rise  in 
both.  Notice  that  the  fluid  rises  highest 
in  the  smallest  tube— just  twice  as  high 
if  one  tube  is  exactly  one-half  diameter 
of  the  other.  (See  Coolers  Philosophy.} 


WATER. 


Mobility.  Ex.  28. — Fill  three  goblets,  one  with  small 
marbles  or  large  peas,  another  with  fine  shot,  and  a  third 
with  water.  Invert  a  dinner-plate  as  a  cover  over  each. 
By  holding  the  plate  tightly  pressed  upon  the  mouth  of 
the  goblet  with  one  hand,  while  the  goblet  itself  is  grasped 
by  the  other,  both  may  be  turned  over  together  without 
spilling  the  contents  of  the  glass.  Do  this  with  each  in 
turn,  and  the  three  goblets  will  be  left  standing,  full, 
but  bottom  upward,  on  the  plates.  Next  carefully  lift  the 
goblet  containing  the  marbles,  and  notice  how  they  spread 
out  upon  the  plate,  and  see  that  they  do  so  because  they 
are  such  smooth  balls,  without  force  to  hold  them  together. 
Then  lift  the  goblet  containing  shot,  and  notice  that  they 
roll  out  upon  the  plate  in  the  same  way  and  for  the  same 
reason.  Finally  lilt  the  goblet  containing  water,  and 
notice  it,  also,  spread  itself  out  upon  the  plate  just  as  the 
others  did.  "We  may  give  the  same  reason :  water  consists 
of  little,  VEKY  little  smooth  balls,  without  force  enough 
among  them  to  hold  them  together. 

Because  water  consists  of  such  very  small  and  smooth 
bodies,  it  is  able  to  move  about  so  freely  as  it  does.  They 
roll  over  and  around  each  other  with  the  greatest  ease. 
This  freedom  of  motion  among  its  molecules  is  called 
mobility.  (See  Coolers  Phil.,  p.  38.) 

Pressure.  Ex.  29. — Having  a  lamp-chimney,  whose 
lower  end  is  smooth  and  even,  cut  a  circle  of  tin  large 


PHYSICAL   SCIENCE 


enough  to  cover  it.  Make  a  small  hole  in  the  center  of 
the  disk  and  pass  a  string  through  it,  letting  a  knot  in  the 
lower  end  prevent  the  string  from  coming  out. 
Now  run  the  string  through  the  lamp-chimney, 
and  by  means  of  it  hold  the  tin  up  tightly 
against  the  end  of  the  glass  until  it  is  pushed 
down  to  the  middle  of  a  jar  of  water.  Then 
let  go  the  string  (Fig.  5),  and  notice  that  the 
tin — a  heavy  metal — does  not  sink.  Notice 
also  that  there  is  nothing  but  water  to  hold  it 
up.  The  experiment  teaches  that  water  exerts 
an  upward  pressure. 

Ex.  30. — Take  a  glass  tube,  bent  in  two 
places  at  right-angles,*  and  hold  the  finger 
tightly  over  one  end,  or  close  it  with  a  cork.  Let  some 
water,  colored  with  ink  or  cochineal,  be  poured  into  the 
other  end ;  it  will  fill  that  arm  of  the  tube  and  a  part  of 
the  horizontal  portion.  (Fig.  6.) 
Now  let  the  air  slowly  pass  from 
under  the  finger  or  the  cork  at 
the  closed  end,  and  notice  the 
water  moving  downward  in  one 
arm,  sideways  through  the  hori- 
zontal part,  and  upward  in  the 
other  arm  of  the  tube.  By  this 
motion  of  the  water  we  learn  that  it  is  exerting  pressure 
downward,  sidewise,  and  upward,  at  the  same  time. 

Ex.  31. — Place  a  small  block  of  wood  upon  the  surface 

*  A  glass  tube  held  in  the  flame  of  an  alcohol  lamp  until  it  begins  to 
soften  may  be  easily  bent  into  any  required  shape.  Roll  it  in  the  flame  to 
heat  all  sides  alike,  and  when  it  begins  to  yield,  press  it  gently  into  the 
desired  shape. 


Fig.  6. 


WATER. 


of  water  in  a  jar,  and  by  means  of  a  rod  of  wood  or  iron 
try  to  push  it  down  to  the  bottom.  Notice  its  struggles 
to  stay  at  the  top,  and  also  that  there  is  nothing  but 
water  to  push  it  up. 

Ex.  32. — To  the  middle  point  of  a  bar  of  wood  let  a 
cord  be  tied  so  that  the  bar 
will  balance  when  the  string 
is  held  in  the  hand.  This 
bar  is  a  very  good  scale-beam. 
From  one  end  hang  a  stone 
about  the  size  of  a  hen's  egg, 
and  from  the  other  end  hang 
a  small  cup,  into  which  put 
just  sand  enough  to  make  it 
balance  the  stone.  (Fig.  7.) 
Now  let  the  stone  be  made  ^  7- 

to  hang  down  into  a  vessel  of  water.  Notice  that  it  is  no 
longer  balanced  by  the  cup  of  sand :  it  is  lighter  in  the 
water  than  out  of  it.  See  that  it  must  be  the  water  that 
helps  to  hold  it  up. 

From  these  two  experiments  we  learn  that  water  presses 
upward  against  bodies  immersed  in  it. 

Ex.  33.— Fill  a  pitcher  brimful  of  water.  Place  a 
dish  under  the  lip  to  catch  the  water  soon  to  run  over, 
and  smear  the  under  side  of  the  edge  of  the  lip  with  tal- 
low to  prevent  water  from  running  down  the  side  of  the 
pitcher.  Lay  the  block  of  wood  (Ex.  31)  carefully  upon 
the  surface,  and  notice  that  water  runs  over  the  lip.  After- 
ward notice  that  the  upward  pressure  of  water  just  sus- 
tains the  wood,  and  hence  must  just  equal  the  weight  of 
the  block.  Hang  a  cup  from  each  end  of  the  scale-beam ; 
make  them  just  balance.  Now  dry  the  wood  and  put  it 
into  one  cup ;  take  the  water  that  was  pushed  over  the 


30  PHYSICAL   SCIENCE. 

lip  of  the  pitcher  by  it  and  put  it  into  the  other  cup. 
Let  all  this  work  be  very  carefully  done.  Then  notice 
that  the  wood  and  water  just  balance.  We  thus  learn 
that  the  water  displaced  by  a  body  which  floats,  weighs 
just  as  much  as  the  body  itself. 

Ex.  34. — Empty  the  water  from  the  cup  and  make  the 
two  cups  balance  each  other  again.  Then  tie  the  stone 
(Ex.  32)  to  one  end  of  the  ''scale-beam"  by  a  string 
long  enough  to  let  it  hang  down  below  the  cup,  and 
put  sand  into  the  other  cup  to  balance  it.  Next  let  the 
stone  hang  into  the  pitcher  full  of  water  and  catch  the 
liquid  displaced.  Notice  that  the  stone  is  lighter  now 
than  before.  How  much  lighter?  Another  experiment 
will  tell. 

Ex.  35. — Put  the  water  that  was  displaced  by  the  stone 
into  the  cup  above  it,  and  notice  that  the  balance  is  re- 
stored, and  learn  that  the  weight  which  this  heavy  body 
loses  in  water  is  just  equal  to  the  weight  of  water  it  dis- 
places. 


AIR 


Compressibility.  Ex.  36. — Take  a  glass  tube  sev- 
eral inches  long  and  pass  one  end  of  it  tightly  through 
a  cork  which  has  been  selected  to  fit  the  neck  of  a 
via!  Push  the  cork  end  of  this  tube  into  some  colored 
water  and  close  the  other  end  with  the  linger.  Keeping 
the  end  closed,  lift  the  cork  from  the  water,  and  press 
it  tightly  into  the  neck  of  the  vial,  at  the  same  time 
taking  the  finger  from  the  end  of  the  tube.  Notice  now 
that  the  colored  water  stands  some  distance  up  the  tube 
— the  space  below  being  filled  with  air. 
(Fig.  8.) 

Next  slip  the  end  of  a  piece  of  rubber 
tubing  over  the  end  of  the  glass  tube. 
Apply  the  lips  to  the  end  of  this  and  gently 
press  the  breath  into  it.  Notice  that  the 
water  in  the  tube  moves  toward  the  vial. 
But  there  is  no  escape  for  the  air,  and  hence 
it  must  be  crowded  into  smaller  space  than 
it  occupied  before.  We  thus  learn  that  air 
is  compressible.  Fjg.  a 

Expansibility.  Ex.  37. — Now  apply  the  lips  to  the 
rubber  tube  again  and  draw  the  air  out  of  it.  Notice  the 
colored  water  moving  away  from  the  vial,  and  see  that 
the  fir  now  fills  more  space  than  before.  We  thus  learn 
that  air  is  expansible. 


32  PHYSICAL  SCIENCE. 

Elasticity.  Ex.  38.— Using  the  same  apparatus,  let 
the  breath  be  alternately  pressed  gently  into  the  tube  and 
then  withdrawn,  and  notice  the  water  alternately  moving 
back  and  forth  in  the  tube.  The  air  first  yields  to  the 
force  of  the  breath ;  it  then  springs  back  when  the  force 
is  withdrawn.  We  see  that  it  is  elastic. 

Pressure.  Ex.  39. — Place  one  end  of  a  straight  glass 
tube  in  colored  water,  and  with  the  lips  at  the  other  end 
withdraw  the  air.  The  colored  water  is  seen  rising  in  the 
tube.  It  is  pushed  up,  but  notice  that  there  is  nothing  to 
push  it  up  but  the  air  that  rests  upon  the  surface  of  the 
water  in  the  vessel. 

Ex.  40. — Push  a  glass  jar  (a  fruit-can)  down  into  a  pail 
of  water  until  it  is  filled.  Take  hold  of  the  bottom  of  the 
jar  and  lift  it  until  only  the  edge  of  the  mouth  of  it  is 
under  the  water  in  the  pail.  Notice  that  the  jar  is  still 
full  of  water.  Something  holds  the  water  up;  there  is 
nothing  to  do  it  but  air  outside 

If  a  shelf  is  fastened  in  one  side  of  the  pail  just  under 
the  surface  of  the  water,  as  may  be  very 
easily  done,  the  full  jar  may  be  left  mouth 
downward  on  the  shelf;  the  water  will 
not  run  out. 

Ex.  41. — Fit  a  long-necked  bottle  with 
a  cork  through  which  two  tubes  pass. 
Both  tubes  should  reach  some  distance 
into  the  bottle.  One  should  reach  some 
inches  outside,  the  other  must  be  shorter. 
To  the  shorter  one  the  end  of  c.  rubber 
tube  must  be  attached.  Fig.  9  shows  the 
full  arrangement.  Now  let  the  lower  end 
Fl&-9-  of  the  longer  tube  be  put  into  colored 


AIR  33 

water,  the  end  of  the  rubber  tube  in  the  lips,  and  let 
the  air  be  drawn  out  of  the  bottle.  Then  notice  a  pretty 
little  fountain  springing  up  instantly  into  the  bottle. 
There  is  nothing  but  air  to  push  the  water  up. 

These  experiments  teach  us  that  air  resting  upon  the 
surface  of  water,  or,  indeed,  of  any  body,  exerts  a  down- 
ward pressure. 

Ex.  42.— Take  the  straight  glass  tube  used  in  Ex.  39 
and  push  it  nearly  its  whole  length  under  water,  and  then 
place  the  finger  over  one  end  to  close  it.  Lift  the  tube 
out  of  the  water,  open  end  downward,  and  notice  that  the 
water  does  not  run  out  of  it.  There  is  nothing  but  air  to 
keep  it  up  in  the  tube. 

Ex.  43. — Take  a  narrow-necked  bottle,  and  having 
immersed  it  in  a  vessel  of  water  until  it  is  filled,  almost 
cover  it  with  the  finger,  turn  it  mouth  downward,  and  lift 
it  out  of  the  water  entirely.  Notice  the  water  refusing  to 
run  out,  and  that  there  is  nothing  but  air  to  keep  it  in. 

Ex.  44. — Take  a  wzVi-inonthed  bottle,  or  an  ale-glass, 
and  proceed  as  follows :  having  filled  it  with  water,  slip 
a  piece  of  paper  under  its  mouth  and  hold  it  against  the 
glass  until  the  bottle  is  lifted  out  of  the  water. 
The  hand  may  then  be  taken  away  from  the  paper, 
when  the  water  will  be  seen  remaining  up  in  the 
bottle.  (Fig.  10.) 

In  these  experiments  we  see  that  the  air  is  exert- 
ing upward  pressure. 

Ex.  45. — Let  the  wide-mouthed  bottle  used  in  mg' 10' 
the  last  experiment  be  filled  with  water  and  covered 
with  the  small  piece  of  paper  as  before.  Hold  it  in  a 
horizontal  position,  see  that  the  water  does  not  run  out. 
Turn  it  around  to  point  in  various  directions  horizon- 


34:  PHYSICAL   SCIENCE. 

tally;  the  water  is  still  kept  in  by  the  air.  Hold  it 
obliquely  in  various  directions,  and  witness  the  same  re- 
sult. We  thus  see  that  air  exerts  pressure  in  all  these 
directions. 

By  considering  all  these  experiments  on  pressure  to- 
gether, we  are  taught  that  air  exerts  pressure  in  all 
directions. 

The  Pump.  Ex.  46.— Let  a  glass  tube  have  one 
open  end  in  colored  water.  With  the  lips  applied  to 
the  other  end,  take  the  air  out  of  the  tube  above  the 
water,  and  notice  that  the  pressure  of  air  pushes  the 
water  up. 

Ex.  47. — Next  take  a  wire  longer  than  the  tube  and 
wind  cotton  upon  one  end  until  it  is  so  large  that  it  can 
with  some  difficulty  be  drawn  into  the  tube. 
Pass  the  wire  up  through  the  tube,  and, 
taking  hold  of  the  upper  end,  pull  the  cotton 
into  the  other  enr1,  and  then  insert  it  in  the 
colored  water.  «j  xt  pull  the  cotton  upward 
in  the  tube,  an'  see  the  water  following  it. 
(Fig.  11.)  Notice  that  the  air  is  here  taken 
out  of  the  tube  above  the  water  by  lifting  the 
cotton. 

We  thus  learn  that  water  will  be  pushed  up 
in  a  pipe  or  tube  whenever  the  air  within  is  by 
any  means  lifted  out.  This  is  the  principle  of 
the  common pum.p.  (Cooley 's  Philosophy,  p.  31. ) 

The  Siphon.  Ex.  48. — Repeat  Ex.  42,  and  notice 
again  that  the  pressure  of  air  sustains  the  column  of  water 
in  the  tube.  (Fig.  12.)  Study  it  further.  See  that  the 
weight  of  the  water  is  pressing  downward;  that  the 


AIR. 


35 


Fig.  12. 


air  is  pressing  upward,  and  that  the  upward  pressure  is 
strongest. 

Ex.  49. — Take  next  a  glass  tube,  bent  in  the 
form  of  the  letter  (J,  its  arms  being  of  exactly 
equal  length,  and  immerse  it  in  water.  When 
it  is  completely  filled,  close  one  end  with  the 
finger  and  lift  the  tube  from  the  liquid.  Hold 
it  with  open  end  downward;  the  water  does 
not  run  out.  Close  the  other  end  and  open  the 
first ;  the  water  still  remains. 

Now  put  the  forefinger  of  one  hand  exactly     v. 
under  the  middle  of  the  bend  so  that  the  tube 

will  balance,  and  then  very  carefully  take  the 
finger  away  from  the  end  of  the  tube.  Both 
ends  are  now  open  downward  (Fig.  13),  but  still 
the  water  does  not  run  out.  Notice  that  the 
water  in  both  arms  is  pressing  downward — that 
the  air  at  both  ends  is  pressing  upward.  Again, 
see  that  the  downward  pressures,  being  equal, 
overcome  equal  portions  of  the  air  press- 
ures, and  thus  leave  equal  upward  press- 
ures to  keep  the  water  from  running  out. 

Ex.  50.— Take  next  a  bent  tube,  one  arm 
being  longer  than  the  other.  Use  it  exactly  as 
the  tube  was  used  in  the  last  experiment.  The 
water  will  not  remain  in  the  tube  balanced  upon 
the  finger;  notice  it  running  out  of  the  longer 
arm  only!  (Fig.  14.) 

In  this  case  there  is  greater  pressure  of  water 
downward  in  the  long  arm  than  in  the  other; 
it   overcomes   more   of  the   air-pressure.     This 
leaves  more  of  the  air-pressure  upward  against      Fi=- 14 
the  water  in  the  short  arm.     This  stronger  pressure  of 


Pig.  13. 


36 


PHYSICAL   SCIENCE. 


Fig.  15. 


the  air  upward  against  the  water  in  the  short  arm  pushes 
the  water  up  through  it,  over  the  bend  and  out  of  the 
longer  arm.  Such  a  bent  tube,  one 
arm  longer  than  the  other,  is  called  a 
siphon.  It  is  used  to  transfer  liquids 
from  one  vessel  into  another;  let 
another  experiment  show  how  it  is 
used,  thus: 

Ex.  5 1.  —Place  an  empty  jar  (fruit- 
can)  or  other  vessel,  beside  another 
containing  water.  Fill  the  siphon 
with  water  by  immersing  it,  and  close  the  longer  arm  by 
holding  the  finger  over  its  end,  while  the  end  of  the 
shorter  arm  is  being  put  into  the  vessel  of  water.  Let 
the  longer  arm  hang  over  into  the  empty  vessel,  and 
open  its  end.  (Fig.  15.)  The  water  will  continue  to  run 
until  it  stands  at  the  same  height  in  both  vessels.  (See 
Philosophy,  p.  73.) 

The  Effect  of  Heat.  Ex.  52.— Take  a  bottle  con- 
taining some  colored  water,  and  lit  to  it  a  cork  f=jj 
having  a  hole  in  its  center.  Take  the  little  vial 
and  glays  tube  used  in  Ex.  36,  and  pass  the  tube 
through  the  hole  in  the  cork  of  the  bottle  down 
into  the  colored  water  below.  (Fig.  16.)  Now 
apply  the  heat  of  a  lamp-flame  yently  to  the  vial, 
or  pour  warm  water  over  it,  and  notice  bubbles 
of  air  coming  out  of  the  tube  and  up  through 
the  water.  The  vial  and  tube  can  no  longer  hold 
all  the  air  they  did. 

Ex.  53. — Press  a  goblet  bottom  upward  down  ^—~J 
into  a  vessel  of  water.  Sue  that  the  goblet  is  full  Fig'ia 
of  air.  Pour  warm  water  over  the  goblet,  and  notice 


AIR.  37 

bubbles  of  air  coming  out  through  the  water,  showing  that 
the  air  is  made  larger  by  the  warmth.  These  experiments 
teach  that  the  effect  of  heat  upon  air  is  to  expand  it. 

Ex.  54. — If  the  bottle  and  vial,  used  in  Ex.  52,  have 
now  been  standing  some  time  since  the  heat  was  applied, 
the  air  in  the  vial  must  have  grown  cool  again.  Look  at 
the  apparatus,  and  see  the  colored  water  standing  far  in 
the  tube  above  the  fluid  in  the  bottle.  Notice  that  the  air 
has  been  cooling  and  growing  smaller  at  the  same  time. 

Ex.  55. — Pour  now  upon  the  vial  some  cold  water;  see 
the  water  mounting  still  higher,  showing  again  that  as  the 
air  is  cooled  it  gets  smaller. 

"We  are  thus  taught  that  air  contracts  when  heat  is 
withdrawn  from  it. 

Ex.  56. — Place  a  piece  of  candle  about  an  inch  long — 
perhaps  less — upon  a  flat  block  of  wood.  Light  it,  and 
notice  the  flame  burning  steadily.  Now  put 
a  lamp-chimney  over  the  flame,  leaving  one 
edge  of  it  projecting  over  the  edge  of  the  block 
(Fig.  17),  and  'notice  that  the  flame  is  no  longer 
steady.  Its  flickering  shows  that  air  is  coming 
under  the  edge  of  the  chimney  against  it. 

Ex.  57.— Now  let  some  bits  of  light  cot- 
ton  or  feather,  hanging  at  the   end  of  fine 
thread,  be  held  over  the  top  of  the  chimney ;        n*  1T- 
they  will  be  blown  away,  showing  that  air  is  coming  out 
of  the  top  of  the  chimney. 

We  thus  learn  that  heated  air  is  pushed  upward  by  the 
colder  air  beside  it  which  flows  in  at  the  bottom  to  take 
its  place. 

Upon  this  principle  the  production  of  winds  may  bo 
explained.  (Natural  Philosophy,  p.  141.) 


VIBRATION". 


The  Pendulum.  Ex.  58. — Let  a  ball — it  may  be  a 
bullet,  a  ball  of  wood,  or  even  an  apple — be  fastened  to 
the  end  of  a  cord,  the  other  end  of  which  is  to  be  attached 
to  some  fixed  support  above.  This  fixed  support  is  easily 
arranged  by  nailing  a  bar  of  wood  to  the  window-frame, 
so  that  it  will  project  out  some  distance  from  the  wall 
into  the  room.  A  string  may  be  bound  around  the  bar, 
and  the  cord  of  the  ball  may  be  tied  into  this  ring.  By 
this  means  the  ball  is  able  to  swing  freely  beneath  its 
support. 

A  body  hung  so  as  to  be  able  to  swing  freely  under  its 
support,  is  a  pendulum. 

Ex.  59.— Lift  the  ball  several  inches  away  to  one  side 
and  let  it  go.  Notice  it  swinging  back  and  forth  over 
the  same  path.  Such  a  motion  is  called  vibration. 

Ex.  60. — Lift  the  ball  again  to  several  inches;  let  it 
go,  and  catch  it  with  the  other  hand  just  as  it  reaches  the 
point  where  it  would  turn  to  go  back  ;  it  has  swung  once 
over  its  path.  This  one  motion  over  its  path  is  called  a 
vibration. 

Ex.  61. — Take  two  balls  of  equal  length,  one  of  lead, 
another  of  wood,  or,  such  not  being  convenient,  an  apple 
and  a  potato  may  be  used  instead,  only  let  them  be  as 
nearly  of  equal  size  as  possible.  Hang  them  from  the 


VIBRATION.  39 

same  bar,  side  by  side,  with  cords  of  the  same  length. 
Take  one  in  each  hand ;  pull  them  to  the  same  distance, 
and  let  them  both  start  at  the  same  moment.  Notice 
that  they  go  over  their  paths  and  get  back  to  the  hands  at 
the  same  time,  showing  that : 

Pendulums  of  different  materials,  other  things  being 
equal,  vibrate  in  the  same  time. 

Ex.  62. — Take  two  balls  of  the  same  material,  two 
apples,  for  instance,  of  different  sizes,  with  cords  of  equal 
lengths.  Release  them  at  the  same  moment ;  notice  that 
they  get  back  to  the  hand  again  at  the  same  time,  show- 
ing that : 

Pendulums  of  different  sizes,  other  things  being  equal, 
vibrate  in  equal  times. 

Ex.  63. — Take  two  balls  of  the  same  material  and  of 
the  same  size,  but  hang  them  on  cords  of  different  lengths. 
Release  them  both  at  once,  and  notice  the  short  one  vibrat- 
ing faster  than  the  other. 

Ex.  64. — Change  the  lengths  of  the  cords,  but  still 
have  one  shorter  than  the  other,  and  after  every  change 
notice  that  the  shortest  pendulum  vibrates  most  rapidly. 

We  thus  learn  that  the  time  of  vibration  depends  upon 
the  length  of  the  pendulum. 

Ex,  65. — Take  now  two  pendulums,  one  being  just 
four  times  the  length  of  the  other.*  Count  the  number 
of  vibrations  each  one  makes  in  one  minute  by  the  watch 
or  clock. .  Divide  60  by  these  numbers,  to  learn  how  long 
each  one  takes  to  make  one  vibration.  Then  notice  that 

*  Measure  from  the  point  of  support  to  a  point  a  very  trifle  below  the 
middle  of  the  ball 


40  PHYSICAL  SCIENCE. 

the  time  for  the  longer  pendulum  is  just  two  times  as 
great  as  for  the  shorter. 

Length  =4 Time  of  a  vibration  =  2. 

Ex.  66. — Let,  next,  one  pendulum  be  nine  times  as 
long  as  the  other.  Count  and  divide  as  before.  Notice 
that  the  longer  pendulum  takes  three  times  as  long  to 
vibrate. 

Length  =  9 Time  of  a  vibration  =  3. 

Now  compare  the  lengths  of  pendulums  and  the  times 
of  one  vibration,  and  see  that : 

The  time  of  one  vibration  varies  as  the  square  root  of 
the  lengths  of  the  pendulum. 


SOUTsTD. 


Ex.  67. — Strike  the  prongs  of  a  tuning-fork  gently 
upon  the  edge  of  a  table,  and  then  stand  the  other  end 
upon  the  table-top.  The  sound  will  be  distinctly  heard. 
Repeat  the  operation,  and  while  the  sound  is  heard,  bring 
the  edge  of  a  knife-blade  carefully  alongside  of  one  of 
the  prongs,  and  notice  what  a  rattle  it  causes.  The  prong 
is  found  to  be  in  motion,  bounding  back  and  forth  against 
the  blade. 

Ex.  68. — Let  a  bell  be  struck,  and  while  the  sound  is 
heard,  touch  the  bell  gently  with  the  finger,  and  feel  the 
tremulous  motion  while  its  sound  is  heard. 

Ex.  69.— If  the  bell  is  large,  or,  better  still,  if  you  have 
a  glass  bell-jar,  make  a  little  pendulum  of  cork,  and  hang 
it  so  that  it  touches  the  lower  rim  of  the  bell.  When  the 
bell  is  struck,  notice  that  you  not  only  hear  the  sound  but 
at  the  same  time  see  the  tremulous  motion  of  the  ball 
caused  by  the  motion  of  the  bell. 

Ex.  70. — Take  a  piece  of  violin-cord,  or  of  piano-wire, 
somewhat  longer  than  your  table.  Fasten  one  end  to  a 
nail  in  one  end  of  the  table,  and  let  the  other  end  of  the 
cord  pass  over  a  pulley,  or  even  a  projecting  piece  of  board, 
fastened  to  the  other  end  of  the  table,  and  to  this  end  of 
the  cord  hang  a  heavy  weight — a  pail  or  box  filled  with 
sand  or  stones.  Let  two  bridges,  like  the  bridge  of  a 
violin,  be  placed  under  the  cord  near  the  ends  of  the 
table.  The  arrangement  is  now  complete. 


42  PHYSICAL   SCIENCE. 

Pull  the  middle  of  the  cord  to  one  side  and  let  it  go 
again.  Notice  the  sound  that  is  heard,  and  the  motion 
that  is  at  the  same  time  seen. 

In  all  these  experiments  we  find  that  the  sounds  of 
bodies  are  accompanied  by  tremulous  motions  or  vibra- 
tions, which  leads  us  to  infer  that : 

Sounds  are  produced  by  vibrations. 

Ex.  71.— Move  one  of  the  bridges  toward  the  other; 
this  shortens  the  vibrating  part  of  the  cord.  Make  it 
sound  again,  and  notice  that  while  the  cord  is  shorter,  the 
sound  it  makes  is  higher.  Shorten  it  more  yet ;  the  sound 
is  still  higher. 

Ex.  72. — Move  the  bridge  gradually  back  to  its  first 
position,  thus  lengthening  the  vibrating  part  of  the  cord. 
Make  it  sound  after  every  change  in  length,  and  notice 
that  while  the  cord  is  lengthening  the  sound  is  gradually 
getting  lower. 

We  thus  learn  that  the  height  or  pitch  of  sound  pro- 
duced by  a  cord  or  wire  depends  upon  its  length — the 
highest  sound  being  caused  by  the  shortest  cord. 

Ex.  73. — Let  the  bridges  remain  stationary,  and  put 
more  and  more  weight  into  the  box  at  the  end  of  the  cord, 
to  stretch  it  tighter.  Notice  the  sound  after  every  addi- 
tion. It  will  be  found  to  get  higher  and  higher. 

Ex.  74.— Next  take  off  the  weight  gradually,  so  that 
the  cord  will  be  stretched  less  and  less,  and  notice  the 
sound  after  each  loss  of  weight ;  it  will  be  found  to  be 
lower  and  lower. 

From  these  experiments  we  infer  that : 

The  pitch  of  the  sound  of  a  cord  or  wire  depends  upon 
the  weight  or  force  which  stretches  it, — the  higher  sound 
being  produced  when  the  cord  is  most  tightly  stretched. 


SOUND.  4.3 

Ex.  75. — Take  two  cords  of  different  sizes  so  that  they 
may  be  of  different  weights,  and  stretch  them  over  the 
table  side  by  side.  Place  the  bridges  under  both  cords, 
so  that  their  vibrating  parts  shall  be  of  equal  lengths,  and 
finally  hang  equal  weights  at  their  ends.  The  lighter 
cord  will  invariably  give  the  higher  sound.  From  this 
we  infer  that : 

The  pitch  of  sounds  produced  by  different  cords  depends 
upon  their  weights.  Other  things  being  equal,  the  ligh^st 
cord  gives  the  highest  sound. 


LIGHT. 


Jb  OR  experiments  with  light  it  is  very  desirable  to  darken 
the  class-room  and  admit  a  small  beam  of  sunlight  with 
which  to  work.  Choose  a  window  into  which  the  sun- 
light enters  most  directly  at  the  time  the  experiments  are 
to  be  made,  and  prepare  it  as  follows : 

Let  some  boards  be  cut  of  the  right  length,  and  let 
them  be  of  such  number  and  length  that  when  fastened 
together  by  elects  they  will  form  a  shutter  fitting  the  in- 
side of  the  window  and  darkening  it  completely.  At  a 
convenient  distance  from  the  bottom  of  this  shutter  a  hole 
two  or  three  inches  in  diameter  should  be  made,  through 
which  sunlight  may  come.  For  some  experiments  the 
direction  of  the  beam  of  light  passing  through  the  room 
is  a  matter  of  importance.  An  addition  easily  made  to 
the  shutter  will  help  the  operator  to  control  the  direc- 
tion and  change  it  at  will.  Let  a  shelf  be  fastened  to  the 
outside  of  the  shutter,  just  under  the  hole.  Upon  this  shelf 
a  piece  of  looking-glass  may  be  placed.  Now,  by  propping 
up  the  outer  end  of  this  glass,  and  perhaps  one  side  of  it 
also  at  the  same  time,  it  may  be  given  just  the  right  posi- 
tion to  receive  the  sun's  rays  and  throw  them  through  the 
hole  into  the  room.  Any  change  of  position  of  the  glass 
will  change  the  direction  of  the  light.  That  the  glass 
may  be  easily  changed  at  pleasure,  have  a  second  hole  in 
the  shutter  large  enough  to  allow  the  hand  to  pass  out  for 


LIGHT.  45 

the  purpose :  this  hole  may  be  covered  with  black  cloth 
when  not  in  use. 

It  will  not  be  difficult  to  darken  the  other  windows  in 
the  room  by  closing  shutters,  or  drawing  curtains,  or 
perhaps  by  hanging  shawls  over  them. 

With  tins  cheap  and  easily- constructed  arrangement 
many  very  beautiful  experiments  may  be  made  with  the 
greatest  ease.  A  looking-glass,  a  small  concave  mirror,  a 
convex  mirror,  one  csmvex  lens  and  another  concave,  and 
a  gl ass pri sm,  are  the  most  important  pieces  of  apparatus. 
They  can  be  obtained  from  apparatus  dealers  at  small 
cost. 

A  little  time,  a  little  money,  and  a  little  ingenuity 
spent  in  putting  up  and  using  this  apparatus,  will  be 
abundantly  repaid  in  beautiful  results. 

Choose  a  day  when  the  sun  shines  brightly,  and  while 
making  experiments  keep  the  lower  sash  of  the  window 
raised  above  the  hole. 

Ex.  76. — Through  the  hole  in  the  shutter  admit  the 
sunbeam  :  sprinkle  dust  in  the  path  by  striking  two  dust- 
brushes  together  in  front  of  its  entrance.  Notice  the  path 
of  the  sunbeam  shown  by  the  very  beautiful  bar  of  illu- 
mined dust :  it  is  perfectly  straight. 

Ex.  77. — Change  the  inclination  of  the  looking-glass  a 
little,  and  see  the  change  of  direction  of  the  sunbeam  in 
the  room.  But  notice  that  in  every  position  the  beam  of 
of  light  is  straight. 

We  thus  learn  that  light  travels  in  straight  lines. 

Ex.  78. — Hold  the  convex  lens  in  the  beam  of  light 
entering  the  room,  and  see  what  a  curious  change :  Notice 
that  the  light  is  brought  to  a  point  (Fig.  18)  at  some 


46  PHYSICAL   SCIENCE. 

distance  from   the  lens,   and   that  beyond  this  point  it 
widens  out  again. 

A  point  where  light  is  col- 
lected is  called  a  focus.  The 
cone  of  light  going  toward  the 
focus  is  called  a  pencil  of  light : 
the  cone  going  from  the  focus  is 
also  a  pencil.  In  the  first  case 
the  pencil  consists  of  converging 
rays ;  in  the  second  the  pencil 
Fig.  is-  consists  of  diverging  rays. 

Ex.  79. — Place  a  lighted  lamp  or  candle  on  a  table  in 
the  darkened  room.  Hold  a  flat  piece  of  wood,  two  or 
three  inches  in  width,  at  a  convenient  distance  in  front 
of  the  flame  and  catch  its  shadow  upon  a  white  wall  or 
upon  a  piece  of  white  cloth  about  as  far  from  the  wood 
as  the  wood  is  from  the  flame.  Notice  that  the  shadow 
is  made  up  of  two  distinct  parts — a  dark  center  and  a 
much  lighter  fringe  on  each  side. 

Ex.  80. — Form  shadows  of  other  bodies  in  the  same 
way — it  scarcely  matters  what  is  chosen  for  the  purpose. 
The  two  parts  of  the  shadow  will  in  every  case  be  more 
or  less  distinct. 

Now  the  dark  center  is  called  the  umbra  and  the 
lighter  envelope  is  called  the  penumbra.  Every  shadow 
is  made  up  of  these  two  parts. 

Ex.  81. — Place  two  flames  upon  the  table  a  little  dis- 
tance apart,  and  hold  the  flat  piece  of  wood  in  front  of 
them,  and  notice  that  two  shadows  appear  upon  the  wall 
or  screen. 

Ex.  82. — Then  move  the  wood  gradually  toward  the 
screen  and  notice  the  two  shadows  drawing  nearer  to- 


LIGHT.  47 

gether.  At  length  the  two  shadows  will  lie  right  beside 
each  other.  Carry  the  wood  a  little  farther,  and  the  two 
shadows  begin  to  overlap  each  other,  and  we  may  notice 
then  a  single  shadow  made  up  of  the  two,  its  umbra  and 
penumbra  very  distinct. 

The  umbra  in  the  last  experiment  is  the  part  of  the 
shadow  which  gets  no  light  from  either  of  the  flames ;  the 
penumbra  receives  light  from  one  or  the  other,  and  is  not 
so  dark  in  consequence. 

Just  so  the  umbra  in  a  common  shadow  is  the  part 
which  gets  no  light  from  any  part  of  the  flame  which 
casts  it,  while  the  penumbra  is  the  part  which  receives 
light  from  some  part  of  the  flame,  and  is  not  so  dark  on 
that  account. 

Ex.  83. — The  "  dance  of  the  witches  "  may  be  shown 
by  cutting  fantastic  figures  out  of  heavy  card-board  and 
hanging  them  by  slender  rubber  cords  from  a  bar  of  wood, 
by  which  they  can  be  held  between  the  flame  and  the 
screen.  A  dancing  motion  can  be  easily  given  to  these 
figures,  and  the  motion  of  their  shadows  will  present  an 
amusing  spectacle  to  those  sitting  in  front  of  the  screen. 
Two  or  three  flames  a  little  distance  apart  will  multiply 
the  shadows  and  increase  the  amusement. 

Ex.  84.— A  circular  disk  of  card-board,  a  triangular 
piece  of  wood,  a  cubical  block,  a  ball,  and  bodies  of  othe> 
shapes,  may  be  in  turn  held  in  front  of  a  flame  and  thei> 
shadows  formed.  Notice  the  shapes  of  the  shadows :  thej1 
will  change  with  every  change  in  the  position  of  the  ob 
ject.  The  disk,  for  example,  gives  a  circular  shadow 
when  its  side  is  toward  the  light,  but  only  a  dark  line 
when  turned  edgewise.  The  ball,  however,  will  give  a 
circular  shadow  in  all  positions. 

The  sphere  is  the  only  form  which  will  in  all  positions 


48  PHYSICAL   SCIENCE. 

give  a  circular  shadow.     The  earth's  shadow  on  the  moon 

in  an  eclipse  always  has  a  circular  outline,  showing  that 

the  earth  is  a  sphere. 

Ex.  85. — Let  a  beam  of  sunlight  into  the  darkened 

room  and  hold  a  looking-glass  obliquely  in  its  path :  the 
light  will  be  instantly  thrown  from  the 
glass  toward  the  ceiling  or  wall  of  the 
room.  (Fig.  19.)  If  the  air  is  well 
sprinkled  with  dust,  the  bars  of  light 
striking  the  glass  and  thrown  from  its 
surface  will  be  seen  distinctly. 

Ex.  86. — Hold  a  piece  of  bright  tin 
or  of  any  polished  metal  in  place  of  the 
glass,  and  notice  the  same  result. 
F.    19  The  light  which  falls  upon  the  surface 

of  a  body  is  called   the  incident  light: 

that  which  is  thrown  off  is  called  reflected  light. 

Ex.  87. — Place  a  looking-glass  upon  the  floor  with  its 
face  uppermost,  and  upon  a  thick  block  of  wood,  or  a 
book  on  the  floor,  near  one  end  of  the  mirror,  put  a 
lighted  candle.  Standing  on  the  other  side  of  the  glass, 
move  around  until  the  image  of  the  candle  is  distinctly 
seen. 

Ex.  88. — If  the  room  is  not  darkened  you  may  stand  a 
goblet  partly  filled  with  water  upon  the  face  of  the 
looking-glass,  and  then  see  the  goblet  standing  upon  its 
image — one  goblet  seeming  to  stand  erect  upon  another 
bottom  upward  partly  full  of  water. 

Notice  in  these  experiments  that  every  part  of  the 
image  is  just  as  far  behind  the  looking-glass  as  the  cor- 
responding part  of  the  object  is  in  front  of  it,  and  that 
the  image  is  just  as  large  as  the  object. 


LIGHT.  49 

It  is  the  light  going  from  the  object  to  the  glass,  and 
being  reflected  from  its  surface  to  our  eyes,  that  enables 
us  to  see  the  image. 

Ex.  89.— Take  two  looking-glasses  of  considerable  size 
and  stand  them  upon  their  edges  at  right  angles  to  each 
other  on  the  table,  the  room  not  being  darkened.  Let  a 
vase  of  flowers  or  any  other  convenient  object  be  placed 
between  the  two  glasses.  Three  distinct  images  of  the 
object  will  be  seen. 

Ex.  90.— Make  the  opening  between  the  glasses  much 
less  than  a  right  angle,  and  then  put  your  face  half-way 
between  their  ends  and  laugh,  as  few  ever  fail  to  do,  at 
the  circle  of  faces  which  is  seen  in  the  mirrors — a  "sur- 
prise party,"  every  member  of  which  will  laugh  with 
you. 

Ex.  91. — Take  a  bowl  or  basin  in  the  dark  room,  and 
at  a  little  distance  from  it  put  a  candle-flame,  so  that  its 
light  may  pass  over  the  top 
and  strike  the  opposite  side 
just  at  the  bottom,  (a,  Fig. 
20.)  The  whole  bottom 
will  then  be  in  the  shade, 
and  will  look  much  darker 
than  the  side  on  which  the  Fig.  20.  b  a 

light  shines.  Then  pour  water  into  the  bowl  until  it  is 
nearly  filled.  Notice  that  the  light  now  covers  a  part  of 
the  bottom  (a  b)  of  the  vessel. 

We  see  that  in  this  case  the  light  is  bent  out  of  the 
straight  line  on  entering  the  water.  Such  a  bending  of 
light  always  occurs  when  light  passes  from  one  substance 
into  another:  it  is  called  refraction. 


50  PHYSICAL   SCIENCE. 

Ex.  92. — The  room  being  light,  put  a  penny  at  the 
bottom  of  the  empty  bowl,  so  that  as  you  look  over  the 

•-  edge  of  the  vessel  it  is 
just  out  of  sight  (at  a, 
Fig.  21).  Now  pom: 
water  into  the  bowl 
carefully,  so  as  not  to 
disturb  the  penny.  The 
penny  will  very  soon 
Fig.  21.  come  into  view  (at  b), 

no  change  having  occurred  in  the  position  of  the  vessel, 
penny,  or  eyea 

Remember  that  we  see  the  penny  just  as  we  see  every 
thing  else,  ly  light  that  comes  from  it  to  our  eyes.  With- 
out the  water,  this  light,  coining  up  over  the  edge  of  the 
bowl,  goes  above  the  eye ;  for  this  reason  we  do  not  see 
the  penny.  But  when  it  has  to  come  up  out  of  water  the 
light  is  bent  where  it  enters  the  air,  and  then,  coming 
over  the  edge  of  the  bowl,  can  enter  our  eyes  and  enable 
us  to  see  the  penny. 

Ex.  93. — Let  a  convex  lens — a  spectacle  glass  can  be 
used  with  success — be  placed  in  the  opening  in  the 
shutter  of  the  dark  room.  The  hole  should  be  no  larger 
than  the  lens :  it  can  be  made  smaller,  if  need  be,  by  cut- 
ting a  hole  of  the  right  size  in  a  piece  of  card-board,  and 
then  tacking  this  card  over  the  larger  hole  in  the  shutter. 
Let  a  screen  be  made  of  thin  white  muslin  stretched  over  a 
wooden  frame.  Place  this  screen  near  the  lens,  and  move 
it  back  and  forth  until  the  best  effect  is  found.  A  beau- 
tiful inverted  picture  in  miniature  of  all  things  outside 
the  window  will  be  seen  upon  the  screen.  A  sheet  of 
white  paper  may  be  used  instead  of  the  muslin  screen  ;  the 
picture  will  then  be  best  seen  on  the  side  toward  the  lens. 


HEAT. 


Production  of  Heat.  Ex.  94.— Rub  a  metallic  but- 
ton upon  a  smooth  board  briskly;  it  soon  will  become 
quite  hot. 

Ex.  95.— Let  the  finger  of  the  right  hand  be  pressed 
upon  the  coat-sleeve  of  the  other  arm,  or  upon  a  piece  of 
woolen  cloth  fastened  to  the  desk  or  table,  and  then 
rubbed  briskly  back  and  forth.  An  inconvenient  heat  is 
soon  felt. 

We  thus  learn  that  heat  is  produced  by  friction. 

Ex.  96. — Let  a  nail  be  laid  upon  some  hard  surface,  a 
smooth  stone,  or  a  flat-iron,  for  example,  and  then  let  it  be 
struck  several  blows  with  a  hammer  in  quick  succession. 
On  feeling  the  nail,  it  will  be  found  to  be  considerably 
warmed.  Indeed,  it  can,  in  this  way,  be  made  too  hot  to 
be  handled  conveniently. 

We  thus  learn  that  heat  is  produced  by  blows. 

Ex.  97.— Upon  some  large  fragments  of  quick-lime 
lying  on  a  plate,  pour  some  water.  After  a  few  minutes, 
notice  the  lirne  swelling  and  crumbling  to  powder,  while 
large  volumes  of  steam  are  escaping.  Let  the  hand  be 
held  in  this  steam  only  for  an  instant,  or  be  laid  upon  the 
plate  when  the  action  has  ceased,  and  great  heat  will  be 
discovered. 


52  PHYSICAL   SCIENCE. 

The  action  of  the  lime  and  water  is  called  a  chemical 
action,  because  the  nature  of  these  bodies  is  changed. 

Ex.  98. — Into  a  cup  put  a  small  quantity  of  cold  water, 
and  then  add  about  one-fourth  as  much  oil  of  vitriol. 
The  mixture  will  become  intensely  hot.  There  is  a  chem- 
ical action  between  the  two  fluids. 

From  these  experiments  we  learn  that  heat  is  produced 
by  chemical  action.  The  heat  of  all  our  lamp-flames  and 
furnaces  is  produced  by  chemical  action. 

Conduction  of  Heat.  Ex.  99. — Take  an  iron  wire 
and  press  a  bit  of  wax  against  one  side  of  it  at  a  distance 
of  a  few  inches  from  one  end.  Place 
this  end  in  the  flame  of  a  lamp.  (Fig. 
22.)  After  a  few  minutes  the  little 
bit  of  wax,  all  this  time  clinging  to 
the  wire,  will  fall  off.  Now,  the  heat 
must  have  travelled  from  the  flame  gradually  along  the 
wire  until  it  reached  the  wax,  and  then,  by  melting  it, 
caused  its  fall. 

Ex.  100. — Hold  one  end  of  a  brass  rod,  a  few  inches 
long,  in  the  lamp-flame.  After  a  little  waiting  the  rod  in 
the  lingers  at  the  other  end  feels  warm.  In  this  case  the 
heat  has  evidently  travelled  gradually  from  the  flame 
through  the  rod  to  the  fingers. 

When  heat  travels  from  particle  to  particle  gradually, 
as  in  these  experiments,  it  is  said  to  be  conducted.  The 
body  in  which  it  travels  is  called  a  conductor. 

Ex.  101. — Take  the  stem  of  a  tobacco-pipe  and  a  rod 
of  iron  as  nearly  of  the  same  size  as  possible,  and  place 
their  ends  together,  lapping  them  about  an  inch,  and 
binding  them  firmly  with  small  wire.  Next  fasten  a  ball 
of  wax  to  the  under  side  of  each  of  the  rods,  equally 


HEAT.  53 

distant  from  the  middle  point  of  their  junction.  Now,  if 
this  arrangement  is  held  with  the  junction  in  a  lamp 
flame  (Fig.  23),  it  will  not  be  *  u 

long  before  the  ball  of  wax  is  /zf~^ 

melted  from  the  iron,  but  it  ^ifi 

will  take  a  long  time  indeed  ^-^a, 

to   melt    the   ball    from    the  Fig'23' 

pipe-stem.  We  learn  thus  that  the  iron  conducts  heat 
better  than  the  pipe-stem. 

Ex.  102. — Take  two  wires  of  different  metals,  brass 
and  copper,  for  example,  of  the  same  size  and  length. 
Hold  one  wire  in  each  hand,  the  other  end  of  the  wire 
being  in  the  lamp-flame.  The  heat  will  be  found  to  reach 
the  fingers  through  one  of  the  wires  quicker  than  through 
the  other.  The  two  metals  teach  us  that  they  do  not 
conduct  heat  alike. 

Ex.  103. — Let  two  spoons,  one  of  German  silver,  the 
other  of  silver,  be  put  into  the  same  cup  of  hot  water, 
with  their  handles  projecting.  Feel  of  the  upper  ends 
from  time  to  time,  and  notice  that  the  silver  spoon  is 
heated  quickest. 

From  these  experiments  we  learn  that  all  bodies  do  not 
conduct  heat  alike. 

Convection  of  Heat. — Ex.  104. — Fill  a  glass  flask 
two- thirds  full  of  water,  and  place  it  upright  in  a  shallow 
basin  of  sand  standing  on  a  hot  stove.  Very  soon  one 
who  looks  closely  at  the  water  will  see  delicate  currents 
moving  upward  from  the  bottom.  Drop  a  bit  of  blue 
litmus  into  the  water.  It  falls  to  the  bottom  and  slowly 
dissolves.  Blue  clouds  appear,  which,  wafted  upward  by 
the  currents  of  water,  enable  us  to  see  their  motion  dis- 
tinctly. These  upward  currents  are  of  warm  water,  and 


54  PHYSICAL  SCIENCE. 

the  heat  is  being  distributed  throughout  the  water  in  the 
flask  by  their  motion. 

When  heat  travels  by  means  of  currents  in  the  body 
receiving  it,  the  process  is  called  convection. 

Radiation  of  Heat. — Ex.  105. — Heat  an  iron  ball 
or  a  piece  of  stone  in  the  stove  until  nearly  or  quite  red- 
hot.  Let  it  be  brought  out  into  the  room  by  means  of  a 
pair  of  tongs.  Hold  the  hand  at  a  little  distance  above  it, 
on  one  side  of  it  and  on  another,  and  below  it.  Notice 
that  instantly,  no  matter  in  what  direction,  the  heat  of 
the  ball  is  felt.  The  air  is  a  very  poor  conductor,  but  we 
find  heat  going  through  it  in  all  directions  more  swiftly 
than  it  can  go  through  the  very  best  conductor. 

Heat  that  is  thrown  through  poor  conductors  in  all 
directions  is  said  to  be  radiated,  and  the  process  of  dis- 
tributing heat  in  this  way  is  called  radiation. 

Expansion  by  Heat.  Ex.  106. — Take  a  bottle  hav- 
ing a  ground  stopper.  When  the  stopper  is  out,  warm 
the  neck  of  the  bottle  gently  by  wrapping  a  cloth  wet 
with  warm  water  around  it,  and  afterward  put  the  stopper 
in — not  too  tightly — just  so  that  it  fits  the  neck  nicely. 
Let  the  neck  cool  again,  and  when  cold  try  the  stopper. 
Notice  that  it  is  tightly  held — perhaps  it  will  not  come 
out  at  all,  because  the  neck  of  the  bottle  is  so  small  as  to 
grasp  it  too  closely.  Now  wrap  the  neck  again  in  the 
warm  cloth,  and  after  a  little  try  the  stopper;  notice  that 
it  comes  out  easily.  The  heat  seems  to  have  made  the 
neck  larger,  so  as  to  let  the  stopper  out. 

Ex.  107. — Let  a  hole  be  bored  through  a  piece  of  hard 
wood,  just  large  enough  to  allow  a  bullet  or  other  metallic 
ball  to  pass  through,  closely  touching  its  sides.  An  iron. 


HEAT.  55 

rod  may  be  used  instead  of  a  ball  often  more  conveniently. 
Heat  the  ball  or  rod,  and  before  it  gets  hot  enough  to 
burn  the  wood,  try  to  pass  it  through  the  hole.  If  it  has 
been  warmed  enough  you  will  notice  that  the  hole  is  no 
longer  large  enough  to  let  the  body  pass. 

These  experiments  teach  us  that  heat  expands  or  en- 
larges solid  bodies. 

Ex.  108.— Fill  a  bottle  with  cold  water.  Pass  a  piece 
of  glass  tube,  a  few  inches  long,  through  a  cork  fitting  the 
neck  of  the  bottle  nicely,  and  press  the  cork  into 
the  neck.  If  the  bottle  was  brimfull  of  water,  as 
it  ought  to  be,  the  water  will  stand  some  distance 
up  in  the  tube  when  the  cork  is  inserted  (Fig.  24). 
Tie  a  string  around  the  tube  to  mark  the  height 
of  the  water  in  it.  Now  plunge  the  bottle  into  a 
vessel  of  warm  water.  Notice  the  water  quickly 
beginning  to  rise  up  the  tube,  and  continuing  to 
do  so  while  the  heat  is  applied. 

We  see  that  the  water  is  getting  larger  as  it 
becomes  hotter.  Fig.  24. 

Ex.  109.— Another  bottle,  used  in  the  same  way,  with 
some  other  liquid,  as  oil  or  alcohol,  will  show  the  same 
effect ;  the  liquid  will  get  larger  as  it  gets  warmer. 

From  these  experiments  we  learn  that  heat  expands 
liquid  bodies. 

Ex.  110.— Fit  the  neck  of  a  bottle  with  a  cork,  and 
through  this  cork  put  the  end  of  a  glass  tube  several 
inches  long.  Into  another  bottle  put  some  water,  which 
may  be  colored  with  ink,  or  cochineal,  or  litmus.  Turn 
the  first  bottle  bottom  upward,  and  put  the  open  end  of 
its  tube  down  into  the  colored  water  of  the  second. 


56  PHYSICAL   SCIENCE. 

Notice,  before  going  farther,  that  the  upper  bottle  and  its 
tube  are  full  of  air.  Next  pour  warm  water  upon  the 
upper  bottle,  and  notice  numerous  bubbles  of  air  escaping 
through  the  fluid  from  the  lower  end  of  the  tube.  The 
air  is  expanded  by  the  heat. 

Ex.  111.— After  a  little  time,  the  colored  water  will 
rise  some  distance  up  the  tube  in  the  arrangement  used  in 
the  last  experiment.  When  this  is  the  case,  notice  that 
the  tube,  above  the  water,  and  the  bottle  are  full  of  air. 
Now  pour  some  warm  water  again  over  the  bottle,  and 
see  the  water  quickly  driven  down  by  the  expanding  air. 

We  thus  learn  that  heat  expands  air,  and  when  similar 
experiments  have  been  made  with  other  gases,  the  general 
truth  is  found  that  heat  expands  gaseous  bodies. 

Contraction  by  Cooling.    Ex,  112. — The  hot  rod 

of  iron  (Ex.  107)  was  too  large  to  go  through  the  hole  in 
the  hard  wood,  but  now  that  it  is  cold  again,  try  it,  and 
notice  that  it  goes  through  easily  again.  It  has  given 
off  its  heat  and  at  the  same  time  grown  smaller. 

Ex.  113. — Take  the  bottle  and  tube  with  water,  used 
in  Ex.  108 ;  mark  the  height  of  the  water  in  the  tube, 
and  then  place  the  bottle  in  a  vessel  of  cold  water.  Notice 
the  water  falling  in  the  tube,  showing  that  as  the  water  in 
the  bottle  cools  it  grows  smaller. 

If  this  does  not  show  distinctly  the  desired  result,  then 
first  warm  the  bottle  of  water,  and  afterward  put  it  into 
the  vessel  of  cold  water. 

Ex.  114. — Take  the  apparatus  used  in  Ex.  52,  the  col- 
ored water  now  standing  some  distance  up  in  the  tube, 
the  space  in  the  tube  above  the  water  and  in  the  bottle 
being  filled  with  air.  Pour  cold  water  upon  the  upper 
bottle,  and  notice  the  colored  water  quickly  rising  higher 


HEAT.  5f 

in  the  tube.     The  air  is  cooled  by  the  water,  and  we  see 
that  it  at  the  same  time  gets  smaller. 

From  these  experiments  we  learn  that  the  withdrawal 
of  heat  from  bodies  causes  them  to  contract.  We  thus 
find  that  the  hotter  a  body  is  the  larger  it  is,  and  the  con- 
trary— the  colder  it  is,  the  smaller. 

Curious  effects  in  Water.  Ex.  115.— Into  a  com- 
mon bowl  or  basin  put  a  considerable  quantity  of  snow,  or 
ice  shaved  fine  with  a  large  knife,  and  add  about  half  as 
much  common  salt.  Stir  the  mixture  thoroughly;  it  will 
become  nearly  fluid  and  be  intensely  cold.  It  is  called 
a  freezing  mixture.  Fill  a  thimble  with  water,  or  a  pipe- 
bowl,  with  the  hole  in  its  bottom  closed  with  wax,  and 
stand  this  little  dish  in  the  freezing  mixture.  The  water, 
after  a  few  minutes,  will  be  frozen. 

Ex.  116. — Now  take  the  bottle  and  water  (Ex.  108), 
the  fluid  standing  some  distance  up  the  tube,  and  place  it 
in  the  freezing-mixture. 

Notice  first,  that  the  fluid  sinks  in  the  tube,  showing 
that  as  the  water  cools  it  contracts. 

Notice  next,  after  a  little  time  the  fluid  stops  sinking, 
showing  that  as  water  goes  on  cooling  more  yet  the  con- 
traction stops. 

Notice  again,  that  the  water  begins  to  rise  in  the 
tube  again,  showing  that  the  cooling  water  is  now  ex- 
panding. 

Notice  finally,  lhat  ice  begins  to  form  in  the  bottle,  and 
that  while  the  water  is  freezing,  the  water  in  the  tube 
continues  to  rise,  showing  that  water  expands  while 
freezing. 

Ex.  117. — Take  now  the  bottle  containing  ice  from 


58  PHYSICAL   SCIENCE. 

the  freezing-mixture,  aud  put  it  into  a  vessel  of  water 
slightly  warm. 

Notice  the  water  sinking  in  the  tube  while  the  ice  is 
melting,  showing  that  heat  contracts  the  ice  while  it 
melts  it. 

Notice  afterward,  that  the  water  continues  to  sink  in 
the  tube  for  a  little  time,  showing  that  heat  applied  to  ice- 
cold  water  contracts  it. 

Notice  finally,  that  the  water  in  the  tube  begins  to  rise 
again,  showing  that  after  water  has  reached  a  certain 
degree  of  temperature,  heat  expands  it.  (See  Natural 
Philosophy,  p.  240.) 


ELECTRICITY. 


THE  successful  performance  of  experiments  in  electricity 
demands  a  dry  atmosphere  and  dry  material :  dampness  in 
either  may  cause  annoyance  and  even  complete  failure. 
The  winter  season  is  generally  more  favorable  than  the 
summer,  and  an  un ventilated  room,  in  which  the  air  is 
loaded  with  moisture  from  the  lungs  of  many  individuals, 
is  to  be  especially  avoided.  In  a  long,  cold  winter  even- 
ing, when  the  family  are  gathered  around  the  cheerful 
sitting-room  fire,  electrical  experiments  are  most  likely  to 
succeed  admirably.  And  in  a  school- room,  which  has 
been  thrown  open  and  well-ventilated  during  recess,  and 
in  which  a  brisk  tire  is  rapidly  heating  the  atmosphere 
again,  or,  better  still,  in  the  morning  before  the  pupils 
have  had  time  to  load  the  air  with  dampness,  electrical 
experiments  may  be  tried  with  the  best  assurance  of 
success. 

The  following  experiments  are  simple  enough  for  a 
child  to  perform,  and  will  furnish  children  not  only,  but 
older  students  as  well,  with  much  amusement  and  in- 
struction. 

Electricity  produced  by  Friction.    Ex.  118. — 

Take  a  piece  of  thin  and  tough  brown  paper,  about  an 
inch  wide  and  six  inches  long ;  heat  it  thoroughly  by 
holding  it  over  a  hot  stove  or  the  flame  of  a  lamp,  and  then 
holding  it  in  one  hand  by  the  end,  quickly  pull  it  between 


60  PHYSICAL   SCIENCE. 

the  thumb  and  fingers  of  the  other  hand,  thus  rubbing  it 
vigorously.  After  two  or  three  such  rubbings  bring  the 
paper  near  to  the  wall,  and  it  will  instantly  fly  into  con- 
tact with  it,  and  perhaps  if  you  let  go  of  it  you  will  see 
it  clinging  to  the  wall.  It  will  thus  remain  sometimes 
for  several  minutes  as  if  pasted. 

Ex.  119. — Rub  the  paper  a  second  time,  and,  holding 
it  by  one  end  in  one  hand,  bring  the  other  hand  alongside 
of  it  Notice  how  quickly  the  paper  flies  against  the 
fingers,  and  how  strongly  it  is  inclined  to  stay  there. 

Ex.  120. — Procure  a  glass  tube  several  inches  in 
length, — a  lamp-chimney,  if  one  can  be  found  of  conve- 
nient shape  to  rub  easily ;  procure  also  a  piece  of  flannel 
cloth.  Both  should  be  thoroughly  dry.  Holding  the  glass 
in  one  hand,  bring  it  up  very  near  to  the  face;  you  will 
be  able  to  notice  no  effect,  Next  rub  the  glass  vigorously 
with  the  flannel  held  in  the  other  hand,  and  bring  it  after- 
ward near  to  the  face  as  before.  A  sensation  will  now  be 
felt  like  what  would  be  caused  by  drawing  spiders'  webs 
over  the  face. 

Ex.  121. — Rub  the  glass  again  vigorously,  and  after- 
ward bring  it  near  to  the  knuckle  of  your  hand ;  a  crack- 
ling sound  will  be  heard,  and  in  the  dark  little  sparks  of 
light  are  often  seen. 

Ex.  122. — Place  some  very  small  and  light  bits  of 
cotton  upon  the  table.  Thoroughly  rub  the  glass  again, 
and  bring  it  near  to  the  bits  of  cotton  ;  notice  how  quickly 
they  leap  up  to  meet  it. 

Ex.  123. — Let  a  bit  of  cotton  or  downy  feather  be 
floating  in  the  air;  bring  the  glass,  which  has  been  vigor- 
ously rubbed,  near  to  it.  The  cotton  or  the  feather  will 
instantly  dart  against  the  glass  through  considerable  dis- 
tance. 


ELECTRICITY.  61 

Ex.  124. — Any  one  of  the  preceding  experiments  may 
be  made  with  a  stick  of  sealing-wax  in  place  of  the  glass 
tube.  The  same  effect  will  be  produced. 

In  these  experiments  we  see  that  by  rubbing  the  paper, 
the  glass,  or  the  sealing-wax,  a  new  power  seems  to  be 
developed  in  them.  All  the  effects  noticed  are  due  to 
electricity,  and  this  electricity  is  in  such  cases  produced 
by  rubbing,  or,  as  it  is  called,  by  friction. 

Attraction  and  Repulsion.  Ex.  125. — Untwist  a 
silk  thread,  and  take  one  of  its  fine  fibres ;  tie  to  the  end 
of  this  a  very  small  and  light  piece  of  cotton.  Let  another 
person  hold  the  cotton  by  taking  hold  the  other  end  of  the 
thread,  while  you  rub  the  glass  tube  vigorously.  Then 
bring  the  tube  near  to  the  bit  of  cotton.  You  will  see 
the  cotton  fly  quickly  toward  the  glass,  sometimes  through 
a  distance  of  several  inches.  The  cotton  is  attracted  by 
the  glass. 

Ex.  126. — Rub  the  glass  thoroughly  again,  and  again 
bring  it  near  the  cotton ;  the  cotton  will  doubtless  be 
attracted  as  it  was  before.  If  so,  let  it  cling  to  the  glass 
for  some  time;  then  rub -the  tube  again  and  present  it  to 
the  cotton  as  before.  If  the  cotton  is  again  attracted,  let 
it  stay  in  contact  with  the  glass  for  a  time,  and  then  go 
over  the  same  work  again.  After  a  few, — sometimes  only 
one  of  these  trials,  the  cotton  will  refuse  to  again  come  in 
contact  with  the  glass.  As  often  as  the  tube  is  moved 
toward  it,  the  cotton  darts  away.  Not  until  it  has  first 
touched  some  other  body  can  the  cotton  be  made  to  touch 
the  glass. 

In  this  experiment  we  find  the  cotton  driven  away  from 
the  glass  tube ;  it  is  said  to  be  repelled. 

Ex.  127.— Sometimes  the  electricity  may  be  made  so 


62  PF7SICAL   SCIENCE. 

strong  on  the  gla-?&  that  placing  it  on  one  side  of  the  sus- 
pended cotton  and  the  hand  or  piece  of  iron  on  the  other 
side  of  it,  the  little  pendulum  will  fly  quickly  back  and 
forth  between  them  many  times,  being  first  attracted  and 
then  repelled  by  the  electrified  glass. 

We  learn  from  these  experiments  that  electricity  shows 
its  presence  in  two  ways,  viz. :  by  attraction  and  repul- 
sion. 

Ex.  128. — Let  a  long  silk  ribbon,  warm  and  dry,  be 
hung  over  the  forefinger  of  the  left  hand ;  the  two  parts 
will  hang  down  side  by  side  together.  Now  put  the  fore- 
finger of  the  other  hand  between  the  two  parts  of  the 
ribbon  and  press  them  tightly  against  it  with  the  thumb 
and  other  fingers.  Pull  the  ribbon  out  quickly,  rubbing 
the  whole  length  of  its  parts  between  the  fingers ;  repeat 
this  operation  three  or  four  times,  and  then  notice  that 
the  two  parts  of  the  ribbon  will  no  longer  be  willing  to 
touch  each  other.  They  repel  each  other.  Put  the  hand 
between  them,  and  both  quickly  fly  toward  it ;  remove 
the  hand,  and  they  as  quickly  fly  back  again. 

Ex.  129. — Let  one  person  rsb  the  ribbon,  as  in  the 
last  experiment,  while  another  rubs  the  stick  of  sealing- 
wax  with  the  dry  jlannel.  When  both  are  well  electri- 
fied, let  the  sealing-wax  be  brought  between  the  parts  of 
the  ribbon.  They  will  fly  still  farther  apart.  The  electri- 
fied sealing-wax  repels  the  electrified  ribbon. 

Ex.  130. — Now  rub  a  glass  tube,  a  lamp-chimney,  if 
of  convenient  shape,  and  bring  it  between  the  electrified 
branches  of  the  ribbon.  Both  parts  instantly  fly  toward 
the  glass:  the  electrified  glass  attracts  the  electrified 
ribbon. 

We   see   that   the    ribbon   acts   differently   toward   the 


ELECTRICITY.  63 

electrified  glass  and  toward  the  electrified  sealing-wax. 
It  flies  toward  the  first,  and/rom  the  second. 

Ex.  131. — Hang  a  little  ball  of  cotton  to  the  end  of  a 
silk  fibre,  as  in  Ex.  125.  Hub  the  glass,  and  then  bring  it 
in  contact  with  the  ball  until  the  latter  flies  away,  being 
repelled  by  the  electrified  glass.  Rub  the  sealing-wax 
with  flannel,  and  bring  it  toward  the  ball ;  the  ball  will 
quickly  fly  to  meet  it,  being  attracted  by  it.  Again,  we 
see  that  electrified  glass  and  electrified  sealing-wax  act  in 
different  ways ;  when  the  cotton  is  repelled  by  glass  it  is 
attracted  by  sealing-wax. 

Now  whenever  the  electricity  is  like  that  produced  by 
rubbing  glass  it  is  called  positive  electricity,  and  when  it 
is  like  that  produced  by  rubbing  sealing-wax  with  flannel 
it  is  called  negative  electricity. 

The  Electroscope.  Ex.  132.— Eub  the  glass  tube 
or  stick  of  sealing-wax  vigorously,  and  observe  whether 
any  visible  change  whatever  is  produced.  None :  then, 
without  somefarther  trial,  it  is  not  possible  to  tell  whether 
electricity  has  been  developed  or  not. 

It  may  be  brought  near  to  the  face  or  hand,  and  the 
feeling  of  cobwebs,  or  a  snapping  sound,  may  show  that 
the  tube  or  wax  is  electrified,  or  bringing  it  near  to  light 
bodies,  as  cotton,  on  the  table,  electricity  will  show  its 
presence  by  attracting  them.  But  neither  of  these  ways 
is  always  quite  convenient. 

Ex.  133. — Now  take  a  slender  rod  of  some  dry  wood, 
several  inches  long;  make  a  little  ball  of  the  dried  pith 
of  corn  stalk  or  elder,  of  cork,  or  even  of  cotton ;  fasten 
it  to  one  end  of  a  silk  fibre,  and  tie  the  other  end  of  the 
fibre  to  the  other  end  of  the  wooden  rod.  Next  place  the 
rod  upon  the  table,  so  that  the  end  carrying  the  ball  shall 


64:  PHYSICAL   SCIENCE. 

project  some  inches  beyond  the  edge,  or,  what  is  better 
yet,  put  the  wood  up  on  a  pile  of  books,  or  some  other 
support,  above  the  table,  so  that  the  little  ball  may  swing 
clear. 

Now  notice  that  whenever  the  electrified  glass  tube  or 
sealing-wax  is  brought  near  to  this  little  pendulum,  the 
electricity  is  at  once  shown  by  the  motions  of  the  ball, 
which,  if  the  electricity  is  well  developed,  will  fly  toward 
the  tube  or  wax,  and,  after  a  moment's  hesitation,  will 
as  quickly  fly  away  again. 

Ex.  134. — Or,  take  tinfoil,* — a  piece  one-half  inch 
long  and  one-quarter  inch  wide,  and  hang  it  in  place  of 
the  ball  in  the  preceding  experiment,  and  it  will  be  found 
to  show  the  presence  of  electricity  as  well  as  the  other. 

Here  then  notice  these  simple  and  convenient  arrange- 
ments by  which  to  show  the  presence  of  electricity.  Any 
such  instrument  is  called  an  electroscope. 

Ex.  135. — Rub  the  glass  tube  vigorously,  and  then 
bring  it  in  contact  with  the  ball  of  the  electroscope  ;  this 
ball,  remaining  in  contact  only  a  moment,  if  the  tube  is 
well  electrified,  flies  away  again.  We  have  seen  this 
action  in  former  experiments,  but  what  we  wish  to  notice 
now  is  that  the  ball  in  contact  with  the  glass  takes  elec- 
tricity from  it,  so  that  it  is  electrified  in  the  same,  way  as 
the  glass,  or  in  other  words,  positively,  and  that  when  this 
is  the  case,  the  two  bodies  separate,  showing  that  they 
repel  each  other. 

In  this  experiment  we  see  that  two  bodies,  electrified 
with  positive  electricity,  repel  each  other. 

Ex.  136.— Next  rub  the  sealing-wax  vigorously  with 
flannel,  and  hold  it  in  contact  with  the  ball  of  the  elec- 

*  The  thin  metallic  wrapping  found  on  some  kinds  of  packages  at  the 
grocery  store. 


ELECTRICITY.  65 

troscope  until  it  flies  away,  as  it  will  do  after  one  or  more 
trials.  Now.  what  we  must  notice  here  is  that  the  elec- 
tricity of  the  sealing-wax  is  negative,  and  that  the  little 
ball  must  have  the  same  kind  of  negative  electricity  also 
in  it  when  it  flies  away  from  the  wax. 

In  this  experiment  we  see  that  both  bodies,  electrified 
with  negative  electricity,  repel  each  other. 

We  see  from  these  two  experiments  that  when  bodies 
are  electrified  in  the  same  way,  they  repel  each  other. 
Call  this  the  1st  Law. 

Ex.  137.— Eub  the  glass  tube  again,  and  electrify  the 
ball  of  the  electroscope  with  it.  Notice  that  the  little 
ball  is  positive,  because  electrified  from  glass.  Then  rub 
the  sealing-wax  with  flannel,  and  bring  it  near  to  the 
little  ball.  The  ball  darts  instantly  against  the  wax.  The 
wax  is  negative,  the  ball  is  positive,  and  the  two  attract 
each  other. 

Here  we  see  that  two  bodies,  electrified  with  opposite 
kinds  of  electricity,  attract  each  other.  Call  this  the  %d 
Law. 

Ex.  138.— Repeat  the  experiment  with  the  silk  ribbon 
(Ex.  128).  Notice  its  two  branches  repelling  each  other. 
Now,  are  these  branches  electrified  with  the  same  or  with 
opposite  kinds  of  electricity  ?  (1st  Law.) 

Ex.  139.— Can  we  find  out  which  kind  of  electricity 
we  have  in  the  silk  ? 

Rub  the  glass  tube,  and  hold  it  in  contact  with  the  ball 
of  the  electroscope  until  it  flies  away.  We  know  that  the 
ball  is  positive.  Bring  the  silk  ribbon,  whose  branches 
are  repelling  each  other,  near  to  the  positive  ball,  and  see 
how  quickly  the  two  fly  together !  The  positive  ball  is 


66  PHYSICAL   SCIENCE. 

attracted,  and  hence  (2d  Law),  the  silk  must  be  nega- 
tive. 

We  see  then  that  our  little  "electroscope"  not  only 
helps  us  to  detect  the  presence  of  electricity;  it  also 
helps  us  to  tell  which  kind  a  body  is  electrified  with. 
Let  us  try  it. 

Ex.  140. — Take  a  piece,  of  thin  but  strong  brown 
paper;  cut  from  it  a  strip  an  inch  wide  and  sixteen  or 
twenty  inches  long;  thoroughly  dry  and  warm  it,  and 
then  use  it  just  as  the  silk  ribbon  was  used  (Ex.  128). 
After  the  branches  of  the  paper  have  been  drawn  through 
the  fingers  once  or  twice,  they  repel  each  other  strongly. 
Now  what  kind  of  electricity  have  they  ?  Electrify  the 
ball  of  the  electroscope  from  the  sealing-wax  rubbed  with 
flannel ;  the  ball  is  then  negative.  Bring  near  the  ball 
the  paper,  and  see  how  strongly  they  repel  each  other, 
showing  (1st  Law)  that  they  are  in  the  same  condition  • 
the  paper  is  negative. 

Ex.  141, — Electrify  the  ball  of  the  electroscope  from 
glass:  it  is  positive.  Now  rub  the  sealing-wax  with  flan- 
nel, and  notice  that  it  attracts  the  ball,  showing  the  wax 
to  be  negative. 

Pass  the  hand  over  the  surface  of  the  sealing-wax  to 
remove  the  electricity  from  it.  and  then  rub  it  vigorously 
with  a  piece  of  silk.  Electrify  the  ball  of  the  electro- 
scope from  the  glass  again  ;  it  is  positive.  Bring  the 
electrified  wax  near  to  it,  and  then  notice  that  it  now 
repels  the  ball,  showing  the  wax  to  be  positive.  It  ap- 
pears that  the  electricity  of  sealing-wax,  when  rubbed 
with  flannel,  is  positive,  but,  when  rubbed  with  silk,  is 
negative  ! 

Ex.  142. — See  whether  the  electricity  of  glass  is  differ- 
ent when  the  rubber  is  flannel  from  that  when  the  rubber 


ELECTRICITY.  67 

is  silk.  To  do  this  electrify  the  little  ball  from  the 
sealing-  wax,  rubbed  with  flannel,  and  bring  the  electri- 
fied glass  near  to  it. 

Ex.  143. — Take  two  pieces  of  brown  paper,  each 
about  ten  inches  long  by  five  inches  wide ;  make  them 
quite  hot  by  holding  them  over  a  heated  stove  or  the 
flame  of  a  lamp.  Place  them  on  the  table,  or,  still 
better,  on  a  tea-tray,  one  above  the  other,  and  rub  them 
vigorously  with  the  palm  of  the  hand.  If  now  you  take 
hold  of  one  corner  and  lift  them  from  the  table,  you  will 
find  them  clinging  to  each  other.  If  you  try  to  separate 
them  you  will  see  how  strongly  they  attract  each  other, 
and  sometimes  you  may  hear  also  a  crackling  sound  on 
pulling  them  apart. 

Notice  that  the  upper  one  only  was  rubbed  but  that 
both  are  electrified.  And  more,  since  they  attract  each 
other  they  are  electrified  in  different  ways. 

Ex.  144. — Take  two  fresh  sheets  of  paper,  such  as 
described  in  Ex.  143,  and,  having  heated  them  thoroughly, 
put  one  above  the  other  on  a  pane  of  glass.  Rub  the 
upper  sheet  vigorously  with  the  hand.  Taking  hold  of 
one  end,  lift  them  from  the  glass,  and  notice  that  they 
now  repel  each  other. 

If  Experiments  143  and  144  are  repeated,  it  will  be 
found  that  the  papers  whenever  rubbed  while  lying  upon 
the  tea-tray  will  attract,  but  if  rubbed  while  lying  upon 
the  glass  they  repel  each  other. 

Now  the  upper  one  only  is  electrified  by  the  rubbing  • 
the  lower  one  is  electrified  from  the  upper  one.  When 
they  lie  upon  glass  the  lower  one  becomes  electrified  in 
the  same  way  as  the  upper  one,  and  hence  they  repel  (1st 
Law),  but  when  they  lie  upon  the  tea-tray  the  lower  one 


68  PHYSICAL   SCIENCE. 

becomes  electrified  in  the  opposite  way,  and  hence  they 
attract  (2d  Law). 

When  one  electrified  body  electrifies  another  body  near 
to  it,  and  puts  it  into  a  condition  opposite  to  its  own,  it  is 
said  to  act  by  induction.  The  upper  strip  of  paper,  when 
they  were  rubbed  on  the  tea-tray,  electrified  the  lower 
one  by  induction. 

The  full  explanation  of  induction,  or,  as  it  is  now  gen- 
erally called,  polarization,  may  be  left  for  a  higher  course 
of  study. 

Ex.  145. — Having  electrified  the  two  sheets  of  paper, 
show  that  they  are  in  opposite  conditions  by  testing  them 
with  the  electroscope. 


EAST    EXPERIMENTS. 


CHEMISTRY. 


CHEMISTRY. 


THE  following  simple  experiments  in  Chemistry  are 
pretty  and  instructive,  but,  as  a  general  thing,  the  mate- 
rials needed  are  not  so  conveniently  obtained  as  those 
needed  for  the  experiments  in  Natural  Philosophy.  They 
are  not  expensive,  however,  and  what  cannot  be  found  at 
the  village  stores  can  be  sent  from  dealers  in  larger  towns 
on  application. 

Chemical  Action.  Ex.  146. — Put  some  strong  vine- 
gar into  a  goblet — enough  to  fill  it  about  one-quarter  full. 
Take  some  common  "  baking  soda,"  as  much  as  will  lie 
upon  the  end  of  a  case-knife  blade,  and  sprinkle  it  into 
the  vinegar.  A  violent  foaming  will  occur,  continuing 
for  a  time,  and  when  it  stops  the  "  soda  "  will  have  dis- 
appeared. Add  more  "soda,"  little  by  little,  until  the 
fluid  refuses  to  foam;  the  "soda"  last  added  will  then 
remain  in  the  bottom.  Now  notice:  the  soda  has  dis- 
appeared from  view  in  this  action,  while  the  vinegar  (touch 
it  with  the  tongue)  is  so  changed  as  to  be  no  longer  sour. 

Here  then  we  find  a  violent  action  going  on  between 
the  vinegar  and  the  soda,  by  which  the  natures  of  both 
these  substances  are  changed. 

Ex.  147. — Into  a  common  bottle  put  a  few  small 
pieces  of  copper,  and  then  pour  in  upon  them  nitric  acid 
enougli  to  cover  them.  Notice  that  a  violent  action 
quickly  begins.  The  fluid  appears  to  boil.  Its  color  be- 


72  PHYSICAL   SCIENCE. 

comes  deep  blue.  Cherry-red  vapors  till  the  bottle  above 
the  fluid,  and  perhaps  run  over  the  top  of  it  into  the 
room.  The  copper  is,  in  the  mean  time,  being  slowly 
used  up:  it  will  finally  disappear  altogether  if  there  is 
acid  enough  used  for  the  purpose ;  and  when  the  action 
ceases,  there  will  remain  the  quiet  blue  liquid  in  the 
bottle,  with  some  of  the  red  vapors  remaining  in  the  air 
above. 

In  this  experiment  we  again  find  a  violent  action,  by 
which  the  nature  of  the  substances  used  is  changed. 

Ex.  148. — Into  one  goblet  put  three  or  four  drops  of 
hydrochloric  acid :  into  another  put  as  much  ammonia. 
Now  turn  one  of  these  goblets  right  bottom  side  up 
over  the  mouth  of  the  other.  Both  will  be  quickly  filled 
with  white  fumes.  The  acid  and  the  ammonia  are  liquids 
nearly  or  quite  colorless :  they  form,  when  put  together,  a 
vapor  which  is  white. 

Here  also  we  notice  an  action  which  changes  the  nature 
of  substances. 

Ex.  149. — Mix  together  a  half-teaspoonfull  each  of 
sugar  and  potassic  chlorate,  both  powdered,  and  put  the 
mixture  upon  a  common  card.  The  card  may  well  be 
laid  upon  the  top  of  a  goblet  for  support  to  keep  it  off  the 
table.  Now  put  two  or  three  drops  of  sulphuric  acid 
upon  the  mixture.  A  curious  combustion  will  quickly 
follow,  in  which  tongues  of  purple  flame  will  shoot  up 
some  distance  with  considerable  noise. 

When  the  burning  is  over,  look  for  the  sugar  and  the 
chlorate:  both  have  disappeared,  and  nothing  but  a  black 
coal-like  mass  remains  upon  the  card  instead. 

We  notice  that  this  combustion  is  an  action  by  which 
the  natures  of  the  burning  bodies  are  changed. 

Now,  all  such  actions  as  have  been  shown  in  these  ex- 


CHEMISTRY  73 

periments  are  called  Chemical  Actions.  We  therefore 
mean  by  the  terra  chemical  action  any  action  among 
bodies  of  matter  by  which  their  natures  are  changed. 

Combination    and   Decomposition.     Ex.    150. — 

Into  a  small  vial — a  long  and  narrow  one  is  best  for  the 
purpose — put  some  water,  and  then  add  oil  enough  to 
cover  the  water  well.  Being  the  lighter  liquid,  the  oil 
of  course  floats  upon  the  water.  Now  pour  in  a  little 
ammonia  and  shake  the  mixture  thoroughly.  A  soapy 
liquid  will  appear  instead  of  the  oil  and  water.  Indeed, 
the  oil  and  the  ammonia  have  joined  themselves  together 
and  made  a  kind  of  soap  which  mixes  with  the  water. 
Notice  that  this  new  substance,  the  soap,  is  a  very  differ- 
ent thing  from  either  the  ammonia  or  the  oil  which 
make  it. 

Now,  when  two  or  more  substances  disappear  to  form 
a  new  one  different  from  themselves,  they  are  said  to 
combine.  The  new  substance  made  is  called  a  com- 
pound. The  ammonia  and  the  oil  have  combined  to 
form  the  soap,  which  is  a  compound. 

Ex.  151. — Add  to  the  soapy  liquid  just  made  in  Ex. 
150,  a  little  strong  sulphuric  acid.  Shake  them  well 
together.  The  soapy  liquid  will  in  part  or  wholly  dis- 
appear, while  the  oil  will  be  brought  back  again  and  will 
be  seen  floating  upon  the  water  as  before.  Now  we  see 
that  the  sulphuric  acid  must  have  taken  the  ammonia 
away  from  the  oil,  for  the  soapy  substance  is  broken  up, 
the  oil  in  it  coming  back  again. 

When  a  substance  is  separated  into  the  different  ma- 
terials which  compose  it,  as  the  soap  has  been  in  this 
experiment,  it  is  said  to  be  decomposed.  The  substances 
into  which  it  is  separated  are  called  its  constituents.  The 


74  PHYSICAL   SCIENCE. 

soap  was  decomposed  ;  oil  is  one  of  its  constituents,  am- 
monia is  another. 

Acids.  Ex.  152. — Crush  one  or  two  small  pieces  of 
blue-litmus  and  put  the  powder  into  a  goblet  of  water. 
The  litmus  will  dissolve  and  give  a  deep  blue  color  to  the 
water.  Now  add  a  little  strong  vinegar,  and  notice  the 
curious  change  in  color  :  the  blue  turns  to  red. 

Ex.  153. — Into  another  goblet  of  water,  colored  blue 
with  litmus,  put  a  few  drops  of  sulphuric  acid :  the  blue 
is  quickly  changed  to  red. 

Ex.  154. — Into  another  solution  of  blue  litmus  put  a 
few  drops  of  nitric  acid,  and  notice  how  quickly  the  red 
color  appears. 

Ex.  155. — Take  another  goblet  of  litmus,  and  add 
hydrochloric  acid :  the  blue  instantly  gives  place  to  red. 

"We  find  that  there  is  a  class  of  substances  which  are 
able  to  turn  the  color  of  blue  litmus  to  red.  Should  you 
taste  these  substances  you  would  find  them  all  to  be  sour. 
They  have  other  characters  in  common,  but  the  one  most 
conveniently  tested  is  their  power  to  turn  the  blue  color 
of  litmus  to  red.  These  substances  are  called  acids. 

Alkalies.  Ex.  156. — Take  a  goblet  containing  litmus, 
the  color  of  which  has  been  changed  to  red  by  an  acid, 
and  put  into  it  a  little  ammonia.  Notice  that  the  red 
color  changes  back  again  to  blue. 

Ex.  157. — Take  a  common  glass  or  tin  funnel,  stop  its 
neck  by  crowding  some  unsized  paper  (blotting  paper) 
into  it,  and  then  pack  the  funnel  nearly  full  of  wood-ashes. 
Pour  some  warm  water  upon  the  ashes,  and  as  it  runs 
through  them  and  out  of  the  stem  of  the  funnel  catch  it 
in  a  bottle,  through  whose  neck  the  funnel-stem  passes 


CHEMISTRY.  75 

and  upon  which  it  rests      (Fig.  25.)     When  enough  of 
this  liquid  has  been  caught,  pour  it  into  a  goblet  of  litmus 
whose  color  has  been  changed  to  red  by  an  acid,    — 
and  notice  that  the  blue  color  of  the  litmus  is 
restored.     (If  too  much  acid  has  been  added  to 
the  litmus  it  will   be  difficult  to  make  it  blue 
again.) 

We  see  in  these  experiments  that  some  sub- 
stances have  the  power  to  bring  back  the  blue 
color  of  litmus  after  it  has  been  turned  red  by  Fig' 
acids.  Now,  the  most  common  substances  of  this  kind 
are  called  alkalies.  Ammonia  is  an  alkali,  so  are  potash 
and  soda. 

Acid  or  Alkali?  Ex.  158.— Having  a  bottle  and  a 
cork  which  fits  its  neck,  take  a  wire  and  run  one  end  of 
it  through  the  cork,  so  that  when  the  cork  is  put  into  the 
neck  of  the  bottle  the  wire  will  hang  down  some  distance 
inside.  Now  take  the  cork  in  the  hand  and  hold  the 
other  end  of  the  wire  in  the  fire  until  it  is  very  hot. 
Plunge  this  hot  wire  into  a  vessel  of  sulphur.  By  this 
means  considerable  sulphur  will  cling  to  the  wire.  Now 
again  hold  the  end  of  the  wire  in  fire  to  inflame  the 
sulphur  upon  it,  and  then  plunge  the  burning  sulphur 
into  the  bottle.  It  will  continue  to  burn  for  a  little  while, 
filling  the  bottle  with  white  fumes.  These  white  fumes 
are  quite  different  from  either  the  sulphur  or  the  air :  a 
new  compound  has  been  formed  by  the  burning  sulphur. 

Remove  the  cork  and  wire  and  pour  a  little  blue-litmus 
water  into  the  bottle.  Shake  it  well,  putting  the  hand 
over  the  mouth  of  the  bottle  to  keep  the  contents  from 
escaping,  and  notice  the  change  of  color.  Is  the  new 
compound  an  acid  or  an  alkali  ? 


76  PHYSICAL   SCIENCE. 

The  name  of  this  new  substance  is  sulphurous  acid.  The 
same  white  fumes  are  made  when  a  match  is  lighted. 

Ex.  159. — Put  some  water  into  a  goblet,  and  mix  with 
it  just  enough  blue  litmus  to  give  it  a  distinctly  blue  color. 
Then  take  a  glass  tube:  put  one  end  into  the  colored 
water,  the  other  into  the  mouth,  and  breathe  the  air  from 
the  lungs  out  through  it  in  bubbles  through  the  water. 
After  a  little  while  notice  the  change  in  the  color  of  the 
water :  it  turns  to  red. 

This  experiment  shows  that  an  acid  is  contained  in  the 
breath  as  it  comes  from  the  lungs :  it  is  called  carbonic  acid. 

Nitrogen  and  Oxygen.  Ex.  160. — Prepare  a  bot- 
tle, with  cork  and  wire,  just  as  was  done  in  Ex.  158  ;  the 
bottle  may  be  in  this  case  a  large  one.  Cover  the  end  of 
the  wire  with  sulphur,  and  let  it  burn  in  the  bottle,  as  in 
the  other  experiment.  Have  a  second  cork  fitting  the 
bottle :  take  the  cork  and  wire  out,  putting  the  other  cork 
quickly  in.  Cover  the  wire  a  second  time  with  sulphur, 
and  burn  it  in  the  bottle.  Repeat  this  until  the  sulphur 
quite  refuses  to  burn  in  the  bottle.  Then  turn  the  bottle 
cork  downward :  plunge  its  neck  into  a  basin  of  water : 
take  the  cork  out,  being  careful  to  let  no  air  get  in,  and 
leave  the  bottle  thus  inverted  in  the  water.  After  some 
considerable  time,  notice  that  the  white  fumes  in  the  bot- 
tle are  not  as  dense  as  they  were.  We  see  that  the  water 
is  taking  them  out.  Finally,  they  will  all  disappear. 
Notice  then  that  the  water  has  risen  in  the  bottle  a  ways, 
and  that  the  air  (as  it  seems  to  be)  above  the  water  is 
again  clear.*  Now  cork  the  bottle  again,  and  afterward 
remove  it  from  the  water  and  stand  it  upon  the  table. 

*  If  the  teacher  will  perform  this  part  of  the  experiment  beforehand,  he 
need  not  wait  for  the  water  to  take  the  fumes  out.  He  can  tell  the  pupils 


CHEMISTRY.  ff 

Next  take  a  bit  of  candle ;  fasten  it  to  the  lower  end  of 
a  wire  (which  may  be  bent  upward  for  the  purpose)  (Fig. 
26),  and  having  lighted  it,  take  the  cork  from  the 
bottle  and  plunge  the  candle  in.  The  flame  is  extin- 
guished as  if  it  had  been  plunged  into  water.  If  it 
were  air  in  the  bottle  the  candle  would  continue  to 
burn,  so  that  what  seems  to  be  air  in  the  bottle  is  not. 

Now,  this  gas  is  what  is  called  nitrogen. 

From    this    experiment    several    things    may   be 
learned  : 

Fit st. — The  sulphur,  burned  in  air,  left  only  nitro-Fis-26- 
gen :  then  nitrogen  is  a  constituent  of  air. 

Second. — We  look  at  the  bottle  and  see  that  nitrogen  is 
a  gax,  colorless,  and  transparent  as  air  itself. 

Third. — Nitrogen  extinguishes  flame  as  quickly  as 
water  would. 

Fourth. — The  burning  sulphur  took  something  out  of 
the  air  of  the  bottle  to  leave  the  nitrogen.  This  some- 
thing combined  with  the  sulphur  to  form  the  new  com- 
pound— the  white  fumes. 

Now  this  substance  taken  out  of  the  air  by  the  burning 
sulphur  is  what  is  called  Oxygen.  So  that  we  learn  : 

Fifth. — That  oxygen  is  another  constituent  of  the  air. 

The  sulphur  took  the  oxygen  out  of  the  air  while  burn- 
ing ;  now,  it  is  a  fact  that  when  any  substance  burns  in 
air  the  oxygen  of  the  air  is  being  used  up.  If  it  were  not 
for  the  oxygen  in  the  air  there  would  be  no  such  thing  as 
fire  known  upon  the  earth. 

Ex.  161. — Now  light  the  candle  and  again  plunge  it 

that  he  did  the  same  thing  with  the  other  bottle,  and  that  now,  after  stand- 
ing so  long,  the  fumes  are  all  gone,  and  then  go  on  with  the  work.  Always 
let  the  bottle  which  they  have  been  using,  stand,  that  they  may  see  the  air 
clear  in  it  also  afterward. 


78  PHYSICAL   SCIENCE. 

into  the  bottle  which  held  the  nitrogen  (Ex.  IfiO),  and 
which  has  been  left,  standing  open,  on  the  table.  Notice 
that  the  flame  is  not  quickly  extinguished,  as  it  was  before. 
The  nitrogen  has  left  the  bottle,  we  see :  it  must  have 
(/one  up  out  of  the  open  bottle  into  the  air  of  the  room. 
This  experiment  teaches  us  that  nitrogen  is  lighter  than 


Hydrogen.  Ex.  162. — Put  some  clippings  of  zinc 
(sheets  of  zinc  are  used  under  stoves)  into  a  wide-mouth 
bottle.  Let  the  bottom  of  the  bottle  be  more  than 
covered  with  them,  and  then  pour  water  in  to  more  than 
cover  the  zinc.  Next  pour  a  little  sulphuric  acid  into  the 
bottle.  In  a  few  moments  the  liquid  will  begin  to  foam : 
if  not,  then  add  a  little  more  acid,  for  the  "boiling" 
should  be  violent  enough  to  make  the  foaming  fill  the 
bottle  half  full.  After  this  violent  chemical  action  has 
gone  on  for  a  few  minutes,  and  while  still  violent,  bring  a 
lighted  match  to  the  mouth  of  the  bottle.  An  explosion 
will  be  heard,  and  a  flame  will  at  the  same  time  appear 
at  the  mouth  of  the  bottle — sometimes  running  down 
into  it. 

We  see  that  a  gas  is  produced  in  this  experiment  which 
is  combustible.  This  combustible  gas  is  called  Hydrogen. 

Ex.  163.— Wrap  a  towel  around  a  bottle  containing 
zinc  and  water,  as  in  the  last  experiment.  Pour  in  the 
acid  as  before,  but  touch  the  match  to  the  mouth  of  the 
bottle  very  soon  after  the  action  begins.  The  explosion 
may  be  more  noticeable  in  this  experiment. 

The  object  of  the  cloth  is  to  prevent  the  glass  from 
flying  and  causing  injury  if,  as  very  rarely  occurs,  the 
explosion  should  be  strong  enough  to  break  the  bottle. 
Another  proper  caution  is  to  tie  the  match  to  the  end  of 


CHEMISTRY.  79 

a  wire  or  stick,  so  that  the  hand  would  be  at  a  distance 
when  the  explosion  occurs. 

Now  notice  that  in  this  experiment  the  hydrogen  has 
not  had  time  to  drive  the  air  all  out  of  the  bottle,  so  that 
there  is  a  mixture  of  air  and  the  gas  when  the  explosioc 
occurs. 

We  see  that  hydrogen  and  air  form  an  explosive  mix- 
ture. 

On  this  account  great  care  should  be  taken,  in  all 
experiments  with  hydrogen,  to  expel  all  air  from  the 
apparatus  before  using  the  gas. 

Ex.  164. — Prepare  a  cork  for  the  bottle  in  which 
hydrogen  is  to  be  made,  by  making  a  hole  through  the 
middle  of  it  and  inserting  the  end  of  the  stem  of  a  tobacco- 
pipe,  so  that  when  the  cork  is  put  into  the  neck  of  the 
bottle  it  shall  fit  air-tight — the  pipe-stem  reaching  above 
it.  The  zinc  and  \rater  being  put  into  the  bottle,  add 
enough  sulphuric  acid,  and  then  quickly  insert 
the  cork.  Wait  until  you  are  sure  that  the  air 
has  been  driven  out  by  the  hydrogen,  and  then 
bring  a  lighted  match  to  the  upper  end  of  the 
pipe-stem.  The  hydrogen  takes  fire  as  it  issues, 
and  burns  with  a  steady  flame  (Fig.  27). 

Notice  the  flame,  and  you  will  see  that  it  gives 
a  feeble  light,  but : 

Ex.  165. — Insert  a  small  wire  in  the  flame  and 
you  will  find  it  quickly  glowing  with  a  red  heat. 

The  flame  of  burning  hydrogen  is  the  source  of  little 
light,  but  of  very  intense  heat. 

Carbonic  Acid.  Ex.  166. — Cover  the  bottom  of  a 
glass  jar  (it  may  be  a  common  fruit-can)  with  "  baking 
soda,''  and  pour  upon  it — a  little  at  a  time — some  strong 


80  PHYSICAL   SCIENCE. 

vinegar.  Watch  the  violent  boiling,  or,  as  it  is  properly 
called,  effervescence,  which  occurs.  Take  a  bit  of  candle  ; 
fasten  it  to  the  lower  end  of  a  wire,  which  is  bent  upward 
to  support  it.  Light  the  candle  and  pass  it  down  into 
the  jar :  the  flame  will  be  put  out  as  it  enters  the  gas 
given  off  by  this  chemical  action. 

Notice  also  that  the  gas  in  the  jar  is  colorless  and 
transparent.  Is  it  nitrogen  ?  We  will  see  in  another 
experiment. 

Ex.  167. — Let  the  jar  containing  the  gas  stand  for 
some  time  open  upon  the  table  after  the  effervescence  has 
stopped.  Insert  the  lighted  candle  again :  it  is  seen  to  be 
again  extinguished, — showing  that  this  gas  is  heavier 
than  air,  and  hence  is  not  nitrogen. 

This  colorless  gas,  which  extinguishes  flame  and  is 
heavier  than  air,  is  called  Carbonic  acid. 

Ex.  168. — Take  a  piece  of  candle,  an  inch  in  length, 
and  fasten  it  upon  a  cork.  This  may  be  done  by  dropping 
some  melted  tallow  upon  the  middle  of  the  cork  and 
pressing  the  lower  end  of  the  candle  down  upon  it,  until 
it  hardens.  Light  the  candle,  and  put  it  into  a  jar,  or  very 
wide-mouthed  bottle.  Cover  the  jar  with  a  plate.  The 
candle  standing  upon  the  bottom  of  the  jar  goes  on  burn- 
ing for  a  little  while,  but  begins  to  grow  dim,  and  finally 
expires.  Take  the  plate  from  the  jar.  A  stiff  wire  which 
has  been  sharpened  with  a  file  may  now  be  stuck  down 
into  the  cork,  and  by  this  means  the  candle  may  be  lifted 
out.  Next  pour  a  little  lime-water*  into  the  jar,  and 
notice  that  on  shaking  it  about  it  becomes  milky.  What 

*  Lime-water  may  be  prepared  by  taking  a  little  slacked  lime,  putting  it 
into  a  bottle,  filling  the  bottle  with  water,  and  then  shaking  it  thoroughly. 
Let  the  lime  afterward  settle,  and  then  pour  off  the  clear  water  above  into 
another  vessel  for  use. 


CHEMISTRY.  81 

makes  this  change  ?  Air  will  not  do  it,  Nitrogen  would 
not  stay  in  the  open  jar,  so  that  it  cannot  be  nitrogen ; 
much  less  can  it  be  hydrogen.  The  gas  which  was  in  the 
jar,  to  turn  the  lime-water  milky,  was  colorless ;  it  put 
out  the  flame  of  the  candle,  and  it  was  heavier  than  air. 
It  seems  to  have  been  carbonic  acid  gas.  As  a  matter  of 
fact,  this  gas  is  the  only  one  which  will  turn  lime-water 
milky. 

But  what  produced  this  gas  in  the  jar  ?  It  must  have 
been  the  burning  caudle. 

All  common  flames  like  this  one  produces  carbonic 
acid  gas. 

Ex.  169. — Put  a  little  lime-water  into  a  goblet,  and, 
taking  a  glass  tube,  or  even  a  straw,  put  one  end  into  the 
water,  the  other  into  the  mouth,  and  breathe  the  breath 
out  through  the  liquid.  After  a  breath  or  two,  the  lime- 
water  will  be  seen  to  be  milky,  thus  showing  the  presence 
of  carbonic  acid  gas. 

We  learn  from  this  experiment  that  carbonic  acid  is 
one  of  the  things  given  otf  from  the  lungs  in  breathing. 

Ex.  170. — Breathe  into  a  clean  and  dry  glass  jar  :  its 
sides  are  instantly  covered  with  de\v.  Showing  that 
water-vapor  is  another  thing  given  off"  from  the  lungs  in 
breathing. 

Carbonic  acid  and  water  are  constantly  being  produced 
in  the  process  of  breathing.  The  first  of  these  is  made 
up  of  carbon  and  oxygen :  the  second  of  hydrogen  and 
oxygen.  The  oxygen  for  both  is  furnished  by  the  air 
taken  into  the  lungs :  the  carbon  and  the  hydrogen  are 
furnished  by  waste  particles  or  impurities  of  the  system. 
The  oxygen  from  the  lungs  enters  the  blood-vessels,  and 
goes  throughout  all  parts  of  the  circulation,  meeting  these 
waste  particles  in  its  course.  It  decomposes  them  :  com- 


82  PHYS.CAL   SCIENCE. 

bines  with  their  carbon  and  hydrogen,  and  then,  as  car- 
bonic acid  and  water,  goes  back  to  the  lungs,  from  which 
these  substances  are  thrown  out  into  the  air.  In  this  way 
the  blood  is  purified. 

Flame.  Ex.  171.— Spread  the  wick  of  an  alcohol 
lamp,  so  that,  lighting  it,  a  large  flame  may  be  obtained. 
Plunge  the  sulphur  end  of  a  match  into  the  dark  center 
of  this  flame,  and  notice  that  while  the  wood  burns  in  the 
edge  of  the  flame,  the  more  combustible  end  of  the  match 
does  not  bur?i  in  the  center  of  it. 

Ex.  172. — Take  a  long  splinter  or  rod  of  pine  wood, 
freshly  smoothed,  that  its  surface  may  be  white,  and  lay 
it  horizontally  across  the  alcohol  flame,  just  above  the 
wick.  When  the  stick  begins  to  burn  remove  it,  and 
notice  that  it  is  scorched  in  two  places.  The  part  which 
was  over  the  center  of  the  flame  is  unharmed. 

Ex.  173. — Press  a  piece  of  white  paper,  held  horizon- 
tally, quickly  down  into  the  flame  of  the  alcohol  lamp,  to 
a  place  just  above  the  wick.  As  soon  as  the  scorching 
begins  to  be  seen  through  the  paper  take  it  quickly  away. 
The  paper  will  be  burned  in  the  shape  of  a  ring.  That 
part  which  was  directly  over  the  wick  is  un burned. 

Ex.  174. — The  following  experiment  may  be  added  to 
this  list,  provided  great  care  is  taken  to  follow  directions : 
otherwise  accident  might  happen. 

A  common  dinner-plate,  when  inverted,  gives  us  a  very 
shallow  dish,  the  bottom  of  a  plate  being,  as  you  will  see, 
surrounded  with  a  slightly  elevated  rim.  Put  a  plate  upon 
fee  table,  bottom  upward,  and  pour  alcohol  into  the  shal- 
low dish  thus  obtained,  being  very  careful  that  none  of  the 
fluid  runs  over  upon  the  table  or  even  upon  the  sides  of 
the  plate.  Take  a  cork,  about  an  inch  in  diameter :  put  a 


CHEMISTRY.  83 

little  gunpowder  upon  top  of  it,  and  stand  it  right  in  the 
center  of  the  alcohol  on  the  plate.  Take  a  lighted  match 
and  touch  the  alcohol  ato/ie  edge  of  the  plate  ;  it  will  take 
fire :  the  flame  will  instantly  spread  all  over  the  top  of 
the  plate,  and,  if  no  breeze  waft  it  against  the  cork,  the 
gunpowder  will  remain  some  time,  in  the  center  of  the 
flame,  unharmed ! 

These  experiments  clearly  teach  us  that  the  interior  of 
the  alcohol  flame  is  not  in  a  state  of  combustion.  The 
same  experiments,  except  the  last  one,  may  be  made  with 
a  candle-flame  with  much  the  same  results.  The  interior 
of  all  ordinary  flames  are,  like  that  of  the  alcohol-lamp, 
not  burning.  This  central  part  of  a  flame  consists  of 
combustible  gas,  and  is  surrounded  by  the  burning  en- 
velope. 

Ex.  175. — Repeat  Experiment  164  with  apparatus 
shown  in  Fig.  27.  Having  thus  obtained  a  hydrogen- 
flame,  remember  that  it  is  being  produced  by  the  hydro- 
gen from  the  bottle  and  the  oxygen  in  the  air.  Now,  hold 
over  this  flame  a  clean  and  thoroughly  dry  glass  jar.  Its 
sides  will  be  seen  to  become  instantly  covered  with  dew. 

Now,  this  water  is  the  result  of  the  action  between 
hydrogen  and  oxygen  in  the  flame,  and  hence  the  experi- 
ment teaches  that  water  is  made  up  of  the  two  substances, 
hydrogen  and  oxygen. 

Ex.  176. — JSTow  hold  a  clean  and  dry  jar  in  the  same 
way  over  the  flame  of  the  alcohol-lamp :  its  sides  are  soon 
dimmed  with  dew  also.  Let  the  same  thing  be  done  with 
a  candle  and  with  other  flames.  Water  will  be,  in  every 
case,  deposited  upon  the  sides  of  the  jar. 

But,  since  water  consists  of  hydrogen  and  oxygen,  these 
results  show  that  these  two  substances  take  part  in  the 


84:  PHYSICAL  SCIENCE. 

production  of  the  flames.  Water  is  a  product  of  all 
ordinary  combustion  in  flames  :  the  oxygen  is  furnished 
from  the  air:  the  hydrogen  from  the  body  burning. 

Ex.  177. — Press  the  bottom  of  a  cold  dinner-plate 
down  upon  the  flame  of  a  candle.  A  moment  afterward 
take  the  plate  from  the  flame,  and  notice  the  black  soot 
which  is  collected  where  the  flame  burned  against  it. 
There  is  something  beside  hydrogen  and  oxygen,  we  see, 
taking  part  in  the  production  of  this  flame.  The  black 
soot  is  carbon.  The  flame  of  a  burning  stick,  and  indeed 
almost  any  common  flame,  will  furnish  carbon  upon  a 
solid  body  held  in  it.  And  yet  no  carbon  is  seen  when  a 
flame  burns  freely.  Why  ? 

Ex.  178. — Fix  a  bit  of  candle  upon  a  cork,  by  drop- 
ping a  little  of  the  melted  wax  or  tallow  upon  its  top  and 
pressing  the  bottom  of  the  candle  upon  it  until  cold. 
Light  the  candle  and  stand  it  on  the  table,  and  bring  an 
inverted  glass  jar  down  over  it.  The  candle  will  burn 
freely  for  a  little  while,  but  at  length  it  will  burn  more 
dimly,  and  finally  go  out.  Turn  the  glass-jar  right  side 
up  and  pour  into  it  a  little  lime-water.  Alter  shaking  it 
about  a  little,  the  lime-water  will  become  whitish,  show- 
ing the  presence  of  carbonic  acid. 

Now,  carbonic  acid  consists  of  oxygen  and  carbon,  and 
it  has  been  formed  in  the  flame.  Its  oxygen  has  been 
furnished  by  the  air,  but  its  carbon  must  have  come  from 
the  candle.  And  now  we  see  what  becomes  of  the  carbon 
when  a  flames  burns  freely.  It  combines  with  oxygen  of 
the  air,  and  forms  carbonic  acid  gas,  which,  being  in- 
visible, passes  unseen  off  into  the  air. 

We  see  from  these  experiments  that  water  and  car- 
bonic gas  are  produced  by  the  combustion  in  ordinary 
flames.  The  hydrogen  and  the  carbon  for  these  are  fur- 


CHEMISTRY.  85 

nished  by  the  fuel  which  burns,  while  the  oxygen  comes 
from  the  air.  Combustion  in  all  common  instances  is 
nothing  but  a  chemical  action  between  the  oxygen  of  the 
air  and  the  elements  of  the  fuel. 


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Copies  of  any  of  the  above  books  will  be  sent  prepaid  to  any  address,  on 
receipt  of  the  price,  by  the  Publishers  •' 

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(94) 


Physiology  and   Hygiene 


Kellogg's  First  Book  in   Physiology  and  Hygiene 

Cloth,  ismo,  174  pages 40  cents 

Kellogg's  Second  Book  in  Physiology  and  Hygiene 

Cloth,  I2mo,  291  pages 80  cents 

These  two  books  constitute  an  entirely  new  and  well  graded  series 
for  the  study  of  Physiology  and  Hygiene  in  schools.  The  subjects  are 
treated  in  a  natural  and  logical  order  and  arranged  in  a  form  suitable  for 
class  instruction.  The  important  subjects  of  sanitation  and  temperance 
are  thoroughly  treated  from  a  scientific  and  physiological  standpoint. 

Smith's  Primer  of  Physiology  and   Hygiene 

Cloth,  I2mo,  174  pages 30  cents 

Smith's  Elementary  Physiology  and   Hygiene 

Cloth,  i2mo,  225  pages 50  cents 

A  complete  and  symmetrical  series  in  which  the  important  facts  of 

Physiology  and  Hygiene  are  presented  in  an  interesting  manner.     The 

Primer  is  designed  for  beginners  in  the  study  and  the  second  book  for 

classes  in  the  intermediate  grades. 

Steele's  Hygienic  Physiology 

Cloth,  1 2mo,  400  pages $1.00 

This  standard  text-book  has  been  thoroughly  revised  and  consider- 
ably enlarged.  It  contains  all  the  excellent  and  popular  features  that 
have  given  Dr.  Steele's  Science  Series  such  wide  use  in  schools  throughout 
the  country. 

THE  SAME,  abridged.     Cloth,  I2mo,  192  pages      .         .     50  cents 

Tracy's  Essentials  of  Anatomy,  Physiology  and   Hygiene 

Cloth,  i2mo,  345  pages $1.00 

A  practical,  thorough  and  scientific  text-book  of  an  advanced  grade 

for  the  use  of  classes  in  High  Schools,  Academies,  Normal  Schools,  and 

for  private  students. 

Johonnot  and  Bouton's  How  We  Live 

Cloth,  I2mo,  178  pages 40  cents 

An  elementary  text-book  for  beginners  in  which  special  attention  is 

given  to  the  laws  of  Hygiene. 

Walker's  Health  Lessons 

Cloth,  I2mo,  194  pages  .        ....         .         .         .48  cents 

A  book  for  beginners,  presenting  the  subjects  in  an  interesting  and 

readable  form  suitable  for  supplementary  readings. 


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receipt  of  the  prire,  by  the  Publishers: 

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(95) 


Physical   Geography 


Appletons'   Physical   Geography 

By  JOHN  D.  QUACKENBOS,  JOHN  S.  NEWBERRY,  CHARLES  H. 
HITCHCOCK,  W.  LE  CONTE  STEVENS,  WM.  H.  DALL,  HENRY 
GANNETT,  C.  HART  MERRIAM,  NATHANIEL  L.  BRITTON, 
GEORGE  F.  KUNZ  and  Lieut.  GEO.  M.  STONEY. 

Cloth,  quarto,  140  pages $1 .60 

Prepared  on  a  new  and  original  plan.  Richly  illustrated  with  engrav- 
ings, diagrams  and  maps  in  color,  and  including  a  separate  chapter  on 
the  geological  history  and  the  physical  features  of  the  United  States. 
The  aim  has  been  to  popularize  the  study  of  Physical  Geography  by 
furnishing  a  complete,  attractive,  carefully  condensed  text-book. 

Cornell's   Physical   Geography 

Boards,  quarto,  104  pages $1.12 

Revised  edition,  with  such  alterations  and  additions  as  were  found 
necessary  to  bring  the  work  in  all  respects  up  to  date. 

Hinman's   Eclectic   Physical   Geography 

Cloth,  I2mo,  382  pages $1.00 

By  RUSSELL  HINMAN.  A  model  text-book  of  the  subject  in  a  new 
and  convenient  form.  It  embodies  a  strictly  scientific  and  accurate 
treatment  of  Physiography  and  other  branches  of  Physical  Geography. 
Adapted  for  classes  in  high  schools,  academies  and  colleges,  and  for 
private  students.  The  text  is  fully  illustrated  by  numerous  maps, 
charts,  cuts  and  diagrams. 

Guyot's   Physical   Geography 

Cloth,  quarto,  124  pages $1.60 

By  ARNOLD  GUYOT.  Thoroughly  revised  and  supplied  with  newly 
engraved  maps,  illustrations,  etc.  A  standard  work  by  one  of  the  ablest 
of  modern  geographers.  All  parts  of  the  subject  are  presented  in  their 
true  relations  and  in  their  proper  subordination. 

Monteith's   New   Physical   Geography 

Cloth,  quarto,  144  pages $1.00 

An  elementary  work  adapted  for  use  in  common  and  grammar  schools, 
as  well  as  in  high  schools. 


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receipt  of  the  price,  by  the  Publishers: 

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(98) 


Standard  Text-Books  in   Botany 


Gray's  HOW  Plants  GrOW.      (Introductory  Book)  . 

Gray's  How  Plants  Behave 

For  Beginners  in  Primary  and  Intermediate  Schools. 
Gray's  Lessons  in  Botany.     (Revised)        .... 
Gray's  Field,  Forest  and  Garden  Botany.     (Flora)     . 
Gray's  School  and  Field  Botany.     (The  Standard  Text-Book) 

For  Students  in  High  Schools,  Academies  and  Seminaries. 

Gray's  Manual  of  Botany.     (Flora) 

Gray's  Lessons  and  Manual.     (In  one  volume)    . 

For  Advanced  Students,  Teachers,  and  Practical  Botanists. 
Coulter's  Botany  of  the  Rocky  Mountains 

A  flora  adapted  to  the  mountain  section  of  the  United  States. 

Gray  and  Coulter's  Text-Book  of  Western  Botany    . 

Being  Gray's  Lessons  and  Coulter's  Manual  bound  in  one  volume. 

Gray's  Structural  Botany 

Goodale's  Physiological  Botany 

Dana's  Plants  and  their  Children 

Herrick's  Chapters  on  Plant  Life 

Hooker's  Botany.      (Science  Primer  Series)    .... 
Hooker's  Child's  Book  of  Nature.     PART  I.    PLANTS 
Steele's  Fourteen  Weeks  in  Botany         .... 
Wood's  How  to  Study  Plants 


Same  as  above  work,  with  added  chapters  on  Physiological  and  Sys- 
tematic Botany. 

Wood's  Lessons  in  Botany.     (Revised) 

Wood's  New  American  Botanist  and  Florist.     (Revised)     . 
Wood's  Descriptive  Botany 

Being  the  flora  of  the  American  Botanist  and  Florist. 
Wood's  Class  Book  of  Botany 

A  standard  work  for  Advanced  Classes  and  for  the  Student's  Library. 

Youmans's  First  Book  in  Botany 

Youmans's  Descriptive  Botany 

Bentley's  Physiological  Botany 

A  sequel  to  Youmans's  Descriptive  Botany. 
Willis's  Practical  Flora 

A  valuable  supplementary  aid  to  any  text-book  in  the  study  of  Botany. 


80  cents 
54  cents 

94  cents 
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$1.80 

$1.62 
$2.16 

$1.62 
$2.16 

$200 

$200 

65  cents 

60  cents 

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44  cents 

$1.00 

$1.00 


90  cents 
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64  cents 
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address  on  receipt  of  the  price  by  the  Publishers  : 

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New  York  •  Cincinnati  »  Chicago 


Concrete   Geometry  for   Beginners 

BY  A.  R.  HORNBROOK,  A.M. 

Teacher  of  Mathematics  in  High  School,  Evansville,  Ind. 
Linen,  12mo,  201   pages.     Price,  75  cents 

This  little  work  has  been  prepared  by  a  practical 
teacher  of  mathematics  as  an  elementary  text-book  for 
beginners  in  the  study.  In  scope,  plan  and  grade,  it  is 
adapted  to  follow  the  course  in  mathematics  usually  pur- 
sued in  Common  and  Grammar  Schools,  or  to  precede  the 
study  of  Demonstrative  Geometry  in  the  High  School. 

Some  of  the  distinctive  methods  illustrated  and  applied 
in  the  book  are  the  following: 

Experimental  Work.  The  work  is  eminently  practical,  its  material 
and  methods  being  the  results  of  actual  experimental  work  in  private  and 
public  schools  in  discovering  the  effects  produced  upon  the  minds  of 
pupils  by  mathematical  instruction,  and  in  seeking  to  adjust  such  instruc- 
tion to  the  mental  capacity  of  the  pupils,  so  that  it  may  be  most  readily 
assimilated  and  understood  by  them. 

Rational  Development.  This  little  book,  without  giving  rules  to  be 
learned  or  formal  modes  of  reasoning  to  be  copied,  leads  the  child  to 
construct,  to  observe,  to  compute,  to  infer  for  himself  and  to  report  the 
result  of  his  operations  in  mathematical  language. 

Progressive  Plan.  The  plan  of  the  book  is  to  follow  the  method  of 
gradually  developing  each  subject  by  questions,  giving  necessary  infor- 
mation and  directions  in  notes,  thus  allowing  full  scope  to  the  skilful 
teacher  who  can  expand  the  subjects  and  adjust  the  material  to  the  special 
needs  of  each  class. 

Laboratory  Methods.  The  use  of  this  convenient  text-book  for  a  few 
weeks  before  taking  up  Demonstrative  Geometry,  will  give  a  class  that 
familiarity  with  geometric  forms  and  facts  which  is  essential  to  logical 
reasoning,  and  will  thus  greatly  increase  the  chances  of  rapid  and  suc- 
cessful work.  The  great  number  of  problems  and  their  very  gradual 
increase  in  difficulty,  admirably  adapt  the  work  for  use  by  the  Laboratory 
Method. 

Copies  of  this  book  will  be  sent  prepaid  to  any  address,  on  receipt  of  the 
price,  by  the  Publishers  : 

American   Book  Company 

New  York  Cincinnati  -  Chicago 


Elementary  Algebra 


Milne's  Elements  of  Algebra 

Cloth,  i2mo,  200  pages  .  .  .  .60  cents 
This  is  a  beginner's  book  intended  for  classes  commenc- 
ing the  study  of  Algebra  in  Common  Schools,  Grammar 
Schools  or  High  Schools.  It  presents  the  elementary  facts 
of  the  science  in  such  a  simple  manner  that  the  pupil's 
interest  will  be  awakened,  and  the  steps  are  so  gradual 
that  his  progress  will  be  easy  and  encouraging.  Abundant 
examples  insure  a  thorough  understanding  of  each  prin- 
ciple presented,  and  the  solutions  required  are  clear  and 
illustrative.  The  use  of  the  book  in  classes  will  lay  a 
sound  foundation  for  more  advanced  work  in  the  study. 

Sabin  and    Lowry's  Elementary   Lessons  in  Algebra 

Cloth,  i2mo,  128  pages  .  *  .  .50  cents 
This  work  is  designed  to  meet  the  demand  for  a  distinctly 
elementary  Algebra  suitable  for  the  higher  Grammar  School 
grades.  It  consists  of  a  series  of  elementary  lessons,  incul- 
cating a  thorough  knowledge  of  algebraic  processes  and 
giving  facility  in  the  use  of  algebraic  symbols.  The  work 
makes  an  easy  transition  from  arithmetic  to  algebraic  pro- 
cesses, and  the  treatment  throughout  is  simple  and  logical. 
The  examples  for  practice  are  numerous  and  well  graded. 


Copies  of  the  above  books,  or  any  of  our  Higher  Algebras  (see  list), 
•will  be  sent  prepaid  to  any  address,  on  receipt  of  the  price,  by  the 
Publishers  : 

American   Book   Company 

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(85) 


Burnet's  Zoology 

FOR 
HIGH    SCHOOLS   AND    ACADEMIES 

BY 

MARGARETTA  BURNET 

Teacher  of  ZoBlogy,  Woodward  High  School,  Cincinnati,  O. 
Cloth,  12mo,  216  pages.     Illustrated.     Price.  75  cents 


This  new  text-book  on  Zoology  is  intended  for  classes 
in  High  Schools,  Academics,  and  other  Secondary  Schools. 
While  sufficiently  elementary  for  beginners  in  the  study  it  is 
full  and  comprehensive  enough  for  students  pursuing  a 
regular  course  in  the  Natural  Sciences.  It  has  been  prepared 
by  a  practical  teacher,  and  is  the  direct  result  of  school-room 
experience,  field  observation  and  laboratory  practice. 

The  design  of  the  book  h  to  give  a  good  general  knowl- 
edge of  the  subject  of  Zoology,  to  cultivate  an  interest  in 
nature  study,  and  to  encourage  the  pupil  to  observe  and  to 
compare  for  himself  and  then  to  arrange  and  classify  his 
knowledge.  Only  typical  or  principal  forms  are  described, 
and  in  their  description  only  such  technical  terms  are  used 
as  are  necessary,  and  these  are  carefully  defined. 

Each  subject  is  fully  illustrated,  the  illustrations  being 
selected  and  arranged  to  aid  the  pupil  in  understanding  the 
structure  of  each  form. 


Copies  of  Burnet's  School  Zoology  -will  be  sent  prepaid  to  any  address, 
on  receipt  of  the  price,  by  the  Publishers: 

American   Book  Company 

New  York  »  Cincinnati  »  Chicago 

(102) 


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